Robustness of ISS systems to inputs with limited moving average: Application to spacecraft formations

We provide a theoretical framework that fits realistic challenges related to spacecraft formation with disturbances. We show that the input‐to‐state stability of such systems guarantees some robustness with respect to a class of signals with bounded average‐energy, which encompasses the typical disturbances acting on spacecraft formations. Solutions are shown to converge to the desired formation, up to an offset, which is somewhat proportional to the considered moving average of disturbances. In the presence of fast peaking perturbations, the approach provides a tighter evaluation of the disturbances' influence, which allows for the use of more parsimonious control gains. Copyright © 2015 John Wiley & Sons, Ltd.     

Path Planning for UAVs Under Communication Constraints Using SPLAT! and MILP

We will in this paper address the problem of offline path planning for Unmanned Aerial Vehicles (UAVs). Our goal is to find paths that meet mission objectives, are safe with respect to collision and grounding, fuel efficient and satisfy criteria for communication. Due to the many nonconvex constraints of the problem, Mixed Integer Linear Programming (MILP) will be used in finding the path. Approximate communication constraints and terrain avoidance constraints are used in the MILP formulation. To achieve more accurate prediction of the ability to communicate, the path is then analyzed in the radio propagation toolbox SPLAT!, and if the UAVs are not able to communicate according to design criteria for bandwidth, constraints are modified in the optimization problem in an iterative manner. The approach is exemplified with the following setup: The path of two UAVs are planned so they can serve as relay nodes between a target without line of sight to the base station.     

Intrinsic isotopic C labelling of polyphenols

The intrinsic isotopic labelling of plants with ¹³CO₂ is an effective method to generate highly labelled compounds using photosynthesis and avoiding labour-intensive complex organic syntheses. In this study, the intrinsic isotopic labelling of polyphenols in parsley, spinach and peppermint is shown for the first time. The plants were grown in an atmosphere where ¹²CO₂ was replaced by ¹³CO₂, in order to generate highly labelled compounds. The total content of ¹³C as well as the individual polyphenols were analysed by Isotopic Ratio-MS and HPLC–Iontrap-MSⁿ.     

Biotic and abiotic determinants of the ascent behaviour of adult Atlantic salmon transiting passable waterfalls

The spawning migration of Atlantic salmon has been characterized by tracking salmon carrying electronic tags as they ascend rivers, but still little is known about how natural obstacles such as waterfalls influence migratory behaviour and how such behaviours are mediated by various biotic (e.g., fish size) and abiotic (e.g., discharge, water temperature, and barometric pressure) factors. The Norwegian river Numedalslågen is interrupted by natural waterfalls ranging in height from 2 to 6 m. We tagged 113 Atlantic salmon with radio transmitters in the estuary and used stationary radio telemetry stations to track fish. Ninety‐one salmon were recorded in Numedalslågen, 39 of which remained in the river for spawning. Large salmon moved farther and faster upriver but also delayed longer and had lower daily probability to pass the second waterfall. Delay below and passage probability at the final, largest waterfall was affected by water discharge, wherein passage occurred when discharge was declining. Barometric pressure also influenced daily probability of ascent, albeit in opposite directions for each waterfall. Importantly, we also found that salmon with surgically implanted radio transmitters moved farther upriver on average and delayed less time below one of the waterfalls than those with externally attached transmitters. Although there is variance in timing arising from individual decision‐making, we showed that natural waterfalls delay progress of Atlantic salmon on their spawning migration and that both biotic (i.e., size) and abiotic (i.e., barometric pressure and discharge) factors influenced the salmon's decisions to pass waterfalls that they encounter.     

Effects of molecular weight and elastic segment flexibility on syneresis in Ca-alginate gels

Syneresis in Ca-alginate gels was studied as a function of the alginate molecular weight and the degree of flexibility of the elastic segments. Small angle X-ray scattering of alginate gels reveals an increased lateral association of junction zones when entering a Ca²⁺ regime giving syneresis. This suggests growth of junction zones to be the primary driving force for syneresis. Ca-alginate gels prepared from alginates with different molecular weights show a reduced syneresis with decreasing M_w. A reduced syneresis is also observed when fractions of a high M_w alginate is replaced by short alginate molecules enriched in guluronate residues. The effect of altering the monomer sequence of the elastic segments spanning the junction zones was studied by converting poly-mannuronate regions to alternating guluronate/mannuronate sequences by the mannuronan C5-epimerase AlgE4. This epimerisation reaction gives a more flexible elastic segment. The epimerased alginates yielded gels with larger syneresis compared to the non-epimerased, native alginate samples. Thus, both molecular weight and elastic segment flexibility are needed in a molecular model for describing syneretic behaviour in alginate gels. These parameters will to a large extent determine to which degree the non-equilibrium nature of the alginate gel is macroscopically expressed (syneresis).     

Model-based design: a report from the trenches of the DARPA Urban Challenge

The impact of model-based design on the software engineering community is impressive, and recent research in model transformations, and elegant behavioral specifications of systems has the potential to revolutionize the way in which systems are designed. Such techniques aim to raise the level of abstraction at which systems are specified, to remove the burden of producing application-specific programs with general-purpose programming. For complex real-time systems, however, the impact of model-driven approaches is not nearly so widespread. In this paper, we present a perspective of model-based design researchers who joined with software experts in robotics to enter the DARPA Urban Challenge, and to what extent model-based design techniques were used. Further, we speculate on why, according to our experience and the testimonies of many teams, the full promises of model-based design were not widely realized for the competition. Finally, we present some thoughts for the future of model-based design in complex systems such as these, and what advancements in modeling are needed to motivate small-scale projects to use model-based design in these domains.     

Grain Size Effects on Mine Water Quality and Acid/Neutral Rock Drainage Production in Kinetic Testing Using Recsk Porphyry Skarn Cu–Zn Deposit Rocks

The quality of mine drainage from sulphide-containing waste rock dumps is controlled by several factors. To characterize the effects of grain size on acid/neutral rock drainage production, kinetic tests were performed on samples from the Recsk porphyry skarn Cu–Zn deposit in Hungary, an area known to generate ARD. Five columns were used, each containing specific grain size ranges (1–2, 2–4, 4–8, 8–16, and 16–32 mm). Prior to the kinetic tests, a static test was performed for each grain size range to obtain total and available neutralizing potential (NP) and acid potential (AP). Total NP and AP values were roughly similar for all grain size ranges, while available NP increased as grain size decreased. The neutralization potential ratio for all grain size ranges was <1, which suggests a potentially acid-producing material. The kinetic tests, however, had contrasting results; a grain size of 1–4 mm produced a circumneutral pH, while grain size groups >4 mm produced pHs from 5.1 down to 3.6. Higher alkalinity values in the leach water were linked to the finer grain samples, primarily producing circumneutral pH. Grain size correlated with the sulphate release rate during the stable release period: the sulphate release rate was less at larger grain sizes. In contrast, sulphide oxidation calculated from oxygen consumption was highest for the intermediate grain size range, followed by the coarser and then the finer grains. The leaching of metals established an increasing concentration with increasing acidity without a very clear relationship to grain size. The established concept of increased metal mobility with decreasing pH applies, regardless of grain size.