Search for: All records

Aggregate DOI for GPS/GNSS stations: Long-term continuous or semi-continuous occupations at multiple locations 

Motivated by distributed data processing applications, we introduce a class of labeled directed acyclic graphs constructed using sequential and parallel composition operations, and study automata and logics over them. We show that deterministic and non-deterministic acceptors over such graphs have the same expressive power, which can be equivalently characterized by Monadic Second-Order logic and the graded µ-calculus. We establish closure under composition operations and decision procedures for membership, emptiness, and inclusion. A key feature of our graphs, calledsynchronized series-parallel graphs(SSPG), is that parallel composition introduces a synchronization edge from the newly introduced source vertex to the sink. The transfer of information enabled by such edges is crucial to the determinization construction, which would not be possible for the traditional definition of series-parallel graphs. SSPGs allow both ordered ranked parallelism and unordered unranked parallelism. The latter feature means that in the corresponding automata, the transition function needs to account for an arbitrary number of predecessors by counting each type of state only up to a specified constant, thus leading to a notion ofcounting complexitythat is distinct from the classical notion of state complexity. The determinization construction translates a nondeterministic automaton withnstates andkcounting complexity to a deterministic automaton with 2ⁿ²states andkncounting complexity, and both these bounds are shown to be tight. Furthermore, for nondeterministic automata a bound of 2 on counting complexity suffices without loss of expressiveness. 

Abstract Disturbances can alter the structure and function of ecosystems. In stream ecosystems, changes in discharge and physicochemistry at short, intermediate, and long recurrence intervals can affect food webs and ecosystem processes. In this paper, we compare pH regimes in streams at La Selva Biological Station, Costa Rica, where episodic acidification frequency across the stream network varies widely due to buffering from inputs of bicarbonate‐rich interbasin groundwater. To examine the effects of acidification on ecosystem structure and function, we experimentally increased the buffering capacity of a headwater stream reach and compared it to an unbuffered upstream reach. We compared these reaches to a naturally buffered and unbuffered reaches of a second headwater stream. We quantified ecosystem structural (macroinvertebrate assemblages on leaf litter and coarse woody debris) and functional responses (leaf litter and coarse woody debris decomposition rates, and growth rates of a focal insect taxon [Diptera: Chironomidae]). Non‐metric multidimensional scaling and analysis of similarity revealed that macroinvertebrate assemblages were relatively homogenous across the four study reaches, although the naturally buffered reach was the most dissimilar. Ecosystem function, as measured by chironomid growth rates, was greater in the naturally buffered reach, while decomposition rates did not differ across the four reaches. Our results indicate that biological assemblages are adapted to pH regimes of frequently acidified stream reaches. Our experiment informs the effects on structure and function at short time scales in streams that experience moderate acidification, but larger magnitude acidification events in response to hydroclimatic change, as projected under climate change scenarios, may induce stronger responses in streams. 

Abstract PLATO (PLAnetary Transits and Oscillations of stars) is ESA’s M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2R$$_\textrm{Earth}$$ $_{\text{Earth}}^{}$) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5%, 10%, 10% for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO‘s target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile towards the end of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases.