5,817 research outputs found
Lazy Abstraction-Based Controller Synthesis
We present lazy abstraction-based controller synthesis (ABCS) for
continuous-time nonlinear dynamical systems against reach-avoid and safety
specifications. State-of-the-art multi-layered ABCS pre-computes multiple
finite-state abstractions of varying granularity and applies reactive synthesis
to the coarsest abstraction whenever feasible, but adaptively considers finer
abstractions when necessary. Lazy ABCS improves this technique by constructing
abstractions on demand. Our insight is that the abstract transition relation
only needs to be locally computed for a small set of frontier states at the
precision currently required by the synthesis algorithm. We show that lazy ABCS
can significantly outperform previous multi-layered ABCS algorithms: on
standard benchmarks, lazy ABCS is more than 4 times faster
Are planetary nebulae derived from multiple evolutionary scenarios?
Our understanding of planetary nebulae has been significantly enhanced as a
result of several recent large surveys (Parker et al., these proceedings).
These new discoveries suggest that the `PN phenomenon' is in fact more
heterogeneous than previously envisaged. Even after the careful elimination of
mimics from Galactic PN catalogues, there remains a surprising diversity in the
population of PNe and especially their central stars. Indeed, several
evolutionary scenarios are implicated in the formation of objects presently
catalogued as PNe. We provide a summary of these evolutionary pathways and give
examples of each. Eventually, a full census of local PNe can be used to
confront both stellar evolution theory and population synthesis models.Comment: 4 pages, 1 figure. To be published in Planetary Nebulae: an Eye to
the Future, Proceedings of IAU Symposium 283, held in Puerto de la Cruz,
Tenerife, Spain, July 25-29 201
The inner environment of Z~CMa: High-Contrast Imaging Polarimetry with NaCo
Context. Z\,CMa is a binary composed of an embedded Herbig Be and an FU Ori
class star separated by au. Observational evidence indicate a complex
environment in which each star has a circumstellar disk and drives a jet, and
the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z\,CMa in the inner 400
au in scattered light.
Methods. We use high contrast imaging polarimetry with VLT/NaCo at and
bands.
Results. The central binary is resolved in both bands. The polarized images
show three bright and complex structures: a common dust envelope, a sharp
extended feature previously reported in direct light, and an intriguing bright
clump located 0\farcs3 south of the binary, which appears spatially connected
to the sharp extended feature.
Conclusions.We detect orbital motion when compared to previous observations,
and report a new outburst driven by the Herbig star. Our observations reveal
the complex inner environment of Z\,CMa with unprecedented detail and contrast.Comment: Accepted for publication in A&A Letter
Dialectica Categories for the Lambek Calculus
We revisit the old work of de Paiva on the models of the Lambek Calculus in
dialectica models making sure that the syntactic details that were sketchy on
the first version got completed and verified. We extend the Lambek Calculus
with a \kappa modality, inspired by Yetter's work, which makes the calculus
commutative. Then we add the of-course modality !, as Girard did, to
re-introduce weakening and contraction for all formulas and get back the full
power of intuitionistic and classical logic. We also present the categorical
semantics, proved sound and complete. Finally we show the traditional
properties of type systems, like subject reduction, the Church-Rosser theorem
and normalization for the calculi of extended modalities, which we did not have
before
Training telescope operators and support astronomers at Paranal
The operations model of the Paranal Observatory relies on the work of
efficient staff to carry out all the daytime and nighttime tasks. This is
highly dependent on adequate training. The Paranal Science Operations
department (PSO) has a training group that devises a well-defined and
continuously evolving training plan for new staff, in addition to broadening
and reinforcing courses for the whole department. This paper presents the
training activities for and by PSO, including recent astronomical and quality
control training for operators, as well as adaptive optics and interferometry
training of all staff. We also present some future plans.Comment: Paper 9910-123 presented at SPIE 201
A Computation of the Maximal Order Type of the Term Ordering on Finite Multisets
We give a sharpening of a recent result of Aschenbrenner and Pong about the maximal order type of the term ordering on the finite multisets over a wpo. Moreover we discuss an approach to compute maximal order types of well-partial orders which are related to tree embeddings
Discrepancies in Determinations of the Ginzburg-Landau Parameter
Long-standing discrepancies within determinations of the Ginzburg-Landau
parameter from supercritical field measurements on superconducting
microspheres are reexamined. The discrepancy in tin is shown to result from
differing methods of analyses, whereas the discrepancy in indium is a
consequence of significantly differing experimental results. The reanalyses
however confirms the lower determinations to within experimental
uncertainties.Comment: submitted to Phys. Rev.
Online and offline representations of biocultural diversity: A political ecology perspective on nature-based tourism and indigenous communities in the Brazilian Pantanal
The concept of biocultural diversity is confronted with contemporary changes that impact
on local communities, such as globalization and digital transformations. Engaging the conceptual
flexibility of ‘biocultural diversity’, we studied nature-based tourism at the intersection of indigenous
communities and the digital realm. We employed a political ecology perspective to examine online
and offline representations of biocultural diversity in the Brazilian Pantanal, one of the biggest
wetlands in the world, and home to groups of peoples known as the Pantaneiros. Data from
interviews with 48 stakeholders in the tourist sector were structured along three ‘myths’—the
Uncivilised, Unrestrained, and Unchanged—for which we have also constructed counter narratives.
Each myth denoted the primacy of biodiversity, and ignored broader dimensions of the Pantanal
as a bioculturally diverse landscape. The relationships of the Pantaneiros with their environment
were found to be intricate and had clear repercussions for tourism, but ironically, reference to the
Pantaneiro culture in nature-based tourism was superficial. Moreover, thriving on the myths, this
form of tourism perpetuates skewed power structures and social inequalities. Lower-class Pantaneiros
likely suffer most from this. We recommend stakeholder engagement with a biocultural design that
facilitates the integration of other-than-biodiversity values, and that thereby promotes sustainability
of the entire social-ecological system
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