16,545 research outputs found
Local abstraction refinement for probabilistic timed programs
We consider models of programs that incorporate probability, dense real-time and data. We present a new abstraction refinement method for computing minimum and maximum reachability probabilities for such models. Our approach uses strictly local refinement steps to reduce both the size of abstractions generated and the complexity of operations needed, in comparison to previous approaches of this kind. We implement the techniques and evaluate them on a selection of large case studies, including some infinite-state probabilistic real-time models, demonstrating improvements over existing tools in several cases
Mechanisms of Surviving Burial: Dune Grass Interspecific Differences Drive Resource Allocation After Sand Deposition
Sand dunes are important geomorphic formations of coastal ecosystems that are critical in protecting human populations that live in coastal areas. Dune formation is driven by ecomorphodynamic interactions between vegetation and sediment deposition. While there has been extensive research on responses of dune grasses to sand burial, there is a knowledge gap in understanding mechanisms of acclimation between similar, coexistent, dune-building grasses such as Ammophila breviligulata (C3), Spartina patens (C4), and Uniola paniculata (C4). Our goal was to determine how physiological mechanisms of acclimation to sand burial vary between species. We hypothesize that (1) in the presence of burial, resource allocation will be predicated on photosynthetic pathway and that we will be able to characterize the C3 species as a root allocator and the C4 species as leaf allocators. We also hypothesize that (2) despite similarities between these species in habitat, growth form, and life history, leaf, root, and whole plant traits will vary between species when burial is not present. Furthermore, when burial is present, the existing variability in physiological strategy will drive species-specific mechanisms of survival. In a greenhouse experiment, we exposed three dune grass species to different burial treatments: 0 cm (control) and a one-time 25-cm burial to mimic sediment deposition during a storm. At the conclusion of our study, we collected a suite of physiological and morphological functional traits. Results showed that Ammophila decreased allocation to aboveground biomass to maintain root biomass, preserving photosynthesis by allocating nitrogen (N) into light-exposed leaves. Conversely, Uniola and Spartina decreased allocation to belowground production to increase elongation and maintain aboveground biomass. Interestingly, we found that species were functionally distinct when burial was absent; however, all species became more similar when treated with burial. In the presence of burial, species utilized functional traits of rapid growth strategy, although mechanisms of change were interspecifically variable
Recovery of the orbital parameters and pulse evolution of V0332+53 during a huge outburst
The high mass X-ray binary (HMXB) V0332+53 became active at the end of 2004
and the outburst was observed at hard X-rays by RXTE and INTEGRAL. Based on
these hard X-ray observations, the orbital parameters are measured through
fitting the Doppler-shifted spin periods. The derived orbital period and
eccentricity are consistent with those of Stella et al. (1985) obtained from
EXOSAT observations, whereas the projected semimajor axis and the periastron
longitude are found to have changed from 484 to 86 lt-s and
from 31310 to 28314, respectively. This would
indicate an angular speed of 1.50.8 yr for
rotation of the orbit over the past 21 years. The periastron passage time of
MJD 533671 is just around the time when the intensity reached maximum and
an orbital period earlier is the time when the outburst started. This
correlation resembles the behavior of a Type I outburst. During outburst the
source spun up with a rate of 8.01 s
day. The evolution of pulse profile is highly intensity dependent. The
separation of double pulses remained almost constant ( 0.47) when the
source was bright, and dropped to 0.37 within 3 days as the source
became weaker. The pulse evolution of V0332+53 may correlate to the change in
dominance of the emission between fan-beam and pencil-beam mechanisms.Comment: 13 pages, 3 figures, accepted for publication in ApJ
Correlation length of hydrophobic polyelectrolyte solutions
The combination of two techniques (Small Angle X-ray Scattering and Atomic
Force Microscopy) has allowed us to measure in reciprocal and real space the
correlation length of salt-free aqueous solutions of highly charged
hydrophobic polyelectrolyte as a function of the polymer concentration ,
charge fraction and chain length . Contrary to the classical behaviour
of hydrophilic polyelectrolytes in the strong coupling limit, is strongly
dependent on . In particular a continuous transition has been observed from
to when decreased from 100% to
35%. We interpret this unusual behaviour as the consequence of the two features
characterising the hydrophobic polyelectrolytes: the pearl necklace
conformation of the chains and the anomalously strong reduction of the
effective charge fraction.Comment: 7 pages, 5 figures, submitted to Europhysics Letter
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