14,696 research outputs found
What majority decisions are possible
Suppose we are given a family of choice functions on pairs from a given
finite set (with at least three elements) closed under permutations of the
given set. The set is considered the set of alternatives (say candidates for an
office). The question is, what are the choice functions c on pairs of this set
of the following form: for some (finite) family of ``voters'', each having a
preference, i.e., a choice from each pair from the given family, c{x,y} is
chosen by the preference of the majority of voters. We give full
characterization
The Belgian repository of fundamental atomic data and stellar spectra (BRASS). I. Cross-matching atomic databases of astrophysical interest
Fundamental atomic parameters, such as oscillator strengths, play a key role
in modelling and understanding the chemical composition of stars in the
universe. Despite the significant work underway to produce these parameters for
many astrophysically important ions, uncertainties in these parameters remain
large and can propagate throughout the entire field of astronomy. The Belgian
repository of fundamental atomic data and stellar spectra (BRASS) aims to
provide the largest systematic and homogeneous quality assessment of atomic
data to date in terms of wavelength, atomic and stellar parameter coverage. To
prepare for it, we first compiled multiple literature occurrences of many
individual atomic transitions, from several atomic databases of astrophysical
interest, and assessed their agreement. Several atomic repositories were
searched and their data retrieved and formatted in a consistent manner. Data
entries from all repositories were cross-matched against our initial BRASS
atomic line list to find multiple occurrences of the same transition. Where
possible we used a non-parametric cross-match depending only on electronic
configurations and total angular momentum values. We also checked for duplicate
entries of the same physical transition, within each retrieved repository,
using the non-parametric cross-match. We report the cross-matched transitions
for each repository and compare their fundamental atomic parameters. We find
differences in log(gf) values of up to 2 dex or more. We also find and report
that ~2% of our line list and Vienna Atomic Line Database retrievals are
composed of duplicate transitions. Finally we provide a number of examples of
atomic spectral lines with different log(gf) values, and discuss the impact of
these uncertain log(gf) values on quantitative spectroscopy. All cross-matched
atomic data and duplicate transitions are available to download at
brass.sdf.org.Comment: 18 pages, 12 figures, 9 tables. Accepted for publication in A&
VAMDC as a Resource for Atomic and Molecular Data and the New Release of VALD
The Virtual Atomic and Molecular Data Centre (VAMDC) (M.L. Dubernet et al.
2010, JQSRT 111, 2151) is an EU-FP7 e-infrastructure project devoted to
building a common electronic infrastructure for the exchange and distribution
of atomic and molecular data. It involves two dozen teams from six EU member
states (Austria, France, Germany, Italy, Sweden, United Kingdom) as well as
Russia, Serbia, and Venezuela. Within VAMDC scientists from many different
disciplines in atomic and molecular physics collaborate with users of their
data and also with scientists and engineers from the information and
communication technology community. In this presentation an overview of the
current status of VAMDC and its capabilities will be provided. In the second
part of the presentation I will focus on one of the databases which have become
part of the VAMDC platform, the Vienna Atomic Line Data Base (VALD). VALD has
developed into a well-known resource of atomic data for spectroscopy
particularly in astrophysics. A new release, VALD-3, will provide numerous
improvements over its predecessor. This particularly relates to the data
contents where new sets of atomic data for both precision spectroscopy (i.e.,
with data for observed energy levels) as well as opacity calculations (i.e.,
with data involving predicted energy levels) have been included. Data for
selected diatomic molecules have been added and a new system for data
distribution and data referencing provides for more convenience in using the
upcoming third release of VALD.Comment: 8 pages, 1 tabl
Reasoning About Strategies: On the Model-Checking Problem
In open systems verification, to formally check for reliability, one needs an
appropriate formalism to model the interaction between agents and express the
correctness of the system no matter how the environment behaves. An important
contribution in this context is given by modal logics for strategic ability, in
the setting of multi-agent games, such as ATL, ATL\star, and the like.
Recently, Chatterjee, Henzinger, and Piterman introduced Strategy Logic, which
we denote here by CHP-SL, with the aim of getting a powerful framework for
reasoning explicitly about strategies. CHP-SL is obtained by using first-order
quantifications over strategies and has been investigated in the very specific
setting of two-agents turned-based games, where a non-elementary model-checking
algorithm has been provided. While CHP-SL is a very expressive logic, we claim
that it does not fully capture the strategic aspects of multi-agent systems. In
this paper, we introduce and study a more general strategy logic, denoted SL,
for reasoning about strategies in multi-agent concurrent games. We prove that
SL includes CHP-SL, while maintaining a decidable model-checking problem. In
particular, the algorithm we propose is computationally not harder than the
best one known for CHP-SL. Moreover, we prove that such a problem for SL is
NonElementarySpace-hard. This negative result has spurred us to investigate
here syntactic fragments of SL, strictly subsuming ATL\star, with the hope of
obtaining an elementary model-checking problem. Among the others, we study the
sublogics SL[NG], SL[BG], and SL[1G]. They encompass formulas in a special
prenex normal form having, respectively, nested temporal goals, Boolean
combinations of goals and, a single goal at a time. About these logics, we
prove that the model-checking problem for SL[1G] is 2ExpTime-complete, thus not
harder than the one for ATL\star
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