237 research outputs found
Characterizing perfect recall using next-step temporal operators in S5 and sub-S5 Epistemic Temporal Logic
We review the notion of perfect recall in the literature on interpreted
systems, game theory, and epistemic logic. In the context of Epistemic Temporal
Logic (ETL), we give a (to our knowledge) novel frame condition for perfect
recall, which is local and can straightforwardly be translated to a defining
formula in a language that only has next-step temporal operators. This frame
condition also gives rise to a complete axiomatization for S5 ETL frames with
perfect recall. We then consider how to extend and consolidate the notion of
perfect recall in sub-S5 settings, where the various notions discussed are no
longer equivalent
Symmetric and Synchronous Communication in Peer-to-Peer Networks
Motivated by distributed implementations of game-theoretical algorithms, we
study symmetric process systems and the problem of attaining common knowledge
between processes. We formalize our setting by defining a notion of
peer-to-peer networks(*) and appropriate symmetry concepts in the context of
Communicating Sequential Processes (CSP), due to the common knowledge creating
effects of its synchronous communication primitives. We then prove that CSP
with input and output guards makes common knowledge in symmetric peer-to-peer
networks possible, but not the restricted version which disallows output
statements in guards and is commonly implemented.
(*) Please note that we are not dealing with fashionable incarnations such as
file-sharing networks, but merely use this name for a mathematical notion of a
network consisting of directly connected peers "treated on an equal footing",
i.e. not having a client-server structure or otherwise pre-determined roles.)Comment: polished, modernized references; incorporated referee feedback from
MPC'0
A Generic Approach to Coalition Formation
We propose an abstract approach to coalition formation that focuses on simple
merge and split rules transforming partitions of a group of players. We
identify conditions under which every iteration of these rules yields a unique
partition. The main conceptual tool is a specific notion of a stable partition.
The results are parametrized by a preference relation between partitions of a
group of players and naturally apply to coalitional TU-games, hedonic games and
exchange economy games.Comment: 21 pages. To appear in International Game Theory Review (IGTR
Ks- and Lp-band polarimetry on stellar and bow-shock sources in the Galactic center
Infrared observations of the Galactic center (GC) provide a unique
opportunity to study stellar and bow-shock polarization effects in a dusty
environment. The goals of this work are to present new Ks- and Lp-band
polarimetry on an unprecedented number of sources in the central parsec of the
GC, thereby expanding our previous results in the H- and Ks-bands. We use
AO-assisted Ks- and Lp-band observations, obtained at the ESO VLT. High
precision photometry and the new polarimetric calibration method for NACO allow
us to map the polarization in a region of 8" x 25" (Ks) resp. 26" x 28" (Lp).
These are the first polarimetric observations of the GC in the Lp-band in 30
years, with vastly improved spatial resolution compared to previous results.
This allows resolved polarimetry on bright bow-shock sources in this area for
the first time at this wavelength. We find foreground polarization to be
largely parallel to the Galactic plane (Ks-band: 6.1% at 20 degrees, Lp-band:
4.5% at 20 degrees, in good agreement with our previous findings and with older
results. The previously described Lp-band excess in the foregound polarization
towards the GC could be confirmed here for a much larger number of sources. The
bow-shock sources contained in the FOV seem to show a different relation
between the polarization in the observed wavelength bands than what was
determined for the foreground. This points to the different relevant
polarization mechanisms. The resolved polarization patterns of IRS 5 and 10W
match the findings we presented earlier for IRS~1W. Additionally, intrinsic
Lp-band polarization was measured for IRS 1W and 21, as well as for other, less
prominent MIR-excess sources (IRS 2S, 2L, 5NE). The new data offer support for
the presumed bow-shock nature of several of these sources (1W, 5, 5NE, 10W, 21)
and for the model of bow-shock polarization presented in our last work.Comment: 19 pages, 18 figure
Secondary analysis of interviews: using codes and theoretical concepts from the primary study
'Trotz der Möglichkeiten, die eine Sekundäranalyse qualitativer Daten bietet, wird diese Methode mit bedenklichem Blick auf viele methodische und forschungsethische Probleme versehen sowie aufgrund mangelhafter Zugänglichkeit und Aufbereitung der Primärdaten in Deutschland wenig angewendet. Die vorherrschende Skepsis gegenüber Sekundäranalysen hängt unseres Erachtens aber auch mit mangelnder praktischer Erfahrung zusammen. Am Beispiel biographischer Interviewdaten einer Längsschnittstudie über die Biographiegestaltung des Übergangs junger Erwachsener von der Schule in den Beruf wollen wir daher zeigen, welche Chancen in der Nutzung von bereits vorhandenen Daten unter bestimmten methodologischen Bedingungen bestehen. Die Nachfrage nach Daten für eine Sekundäranalyse beschränkt sich üblicherweise auf Originaldaten der Primärstudie. Auf Grundlage unserer Erfahrungen kann man jedoch auch Kodierungen und Kategorienschemata des EDV-gestützten Auswertungsverfahrens der Primärstudie nutzen. Darüber hinaus ist sogar eine eher induktive Vorgehensweise unter Einbeziehung theoretischer Konzepte der Primärstudie wie Typologien möglich. Wenn etwa Kategorienschemata die heuristische Funktion eines überdimensionalen 'Karteikastens' mit breiten und nicht a priori theorielastigen Kategorien besitzen, muss deren Nutzung für die Sekundäranalyse nicht im Widerspruch zu einer eher offenen Kodierung im Prozess der Entwicklung von in-vivo-Kategorien stehen.' (Autorenreferat)'In spite of the possibilities which secondary analysis of qualitative data offers, this method is not often used because of the critical attitude towards a lot of methodological and ethical problems, and also on the grounds of the inadequate access to, and preparation of, the primary data in Germany. It is our opinion that the prevailing scepticism towards secondary analysis is also connected with a lack of practical experience. Based on the example of biographical interview data compiled by a longitudinal study of the biographical shaping of the school-to-work transition of young adults, we would like to show the possibilities which exist for making use of pre-existing data under specific methodological conditions. The demand for data for secondary analysis is usually limited to the original data from the primary study. In our experience, though, it is also possible to use the coding and category schemas of the computer-assisted evaluation process of the primary study. Furthermore, with the inclusion of theoretical concepts of the primary study such as typologies it is even possible to use an inductive procedure. For example, provided that category schemas have the same heuristic function as a huge 'filing box' with broad, and not 'a priori' theory-loaded categories, then their use for secondary analysis does not have to conflict with open coding in the process of the development of in-vivo categories.' (author's abstract)
Symmetric and Synchronous Communication in Peer-to-Peer Networks
Motivated by distributed implementations of game-theoretical algorithms, we study symmetric process systems and the problem of attaining common knowledge between processes. We formalize our setting by defining a notion of peer-to-peer networks and appropriate symmetry concepts in the context of Communicating Sequential Processes (CSP) [1]. We then prove that CSP with input and output guards makes common knowledge in symmetric peer-to-peer networks possible, but not the restricted version which disallows output statements in guards and is commonly implemented. Our results extend [2]
Hadronic form factors for rare semileptonic decays
We discuss first results for the computation of short distance contributions
to semileptonic form factors for the rare decays
and . Our simulations are based on RBC/UKQCD's
ensembles with domain wall light quarks and the Iwasaki gauge action.
For the valence -quark we chose the relativistic heavy quark action.Comment: 7 pages, 1 table, 3 figures, presented at the 33rd International
Symposium on Lattice Field Theory (Lattice2015), July 14-18, 2015, Kobe,
Japa
Tracing the merger-driven evolution of active galaxies using the CJF sample
In the context of the evolution of large structures in the Universe, it is
unclear whether active galaxies are a phase which each galaxy undergoes, and
what is the importance of the evolution of black holes in their centers. Binary
black hole (BBH) systems could play a key role in our understanding of the
above question.
We investigate the Caltech-Jodrell Bank flat-spectrum (CJF) sample for
evidence in favor of the merger-driven evolution scheme of active galaxies and
search tracer-systems of AGN evolution and possible indications of BBH
candidates. We discuss the validity and ambiguity of such indications and
formulate a set of selection criteria for the detection of such systems. We
conduct an extensive literature search for all available multi-wavelength
information, concentrating on the optical and infrared regime, in addition to
morphological information of the CJF sources. We analyze the statistics of this
sample, in terms of these properties.
We find 1 ULIRG (Mrk 231) included in the CJF, prototype of a transitory
system. In total 28.6% of the CJF sources with z<0.4 are distorted or have a
companion. Given the unbiased sample used here, this provides strong evidence
for the ubiquity of the merger phenomenon in the context of active galaxies. We
find a correlation between the radio and the near-infrared luminosity for the
high-luminosity sources, interpreted in the context of the interplay between a
star-formation and AGN component. We find a connection between variability and
evolutionary transitory systems, as selected through their near-infrared
colors. We select 28 sources that trace the different evolution phases of an
AGN, as well as a number of the most promising BBH candidates. We find 4
sources with almost periodical variability in the optical and radio on similar
timescales.Comment: 18 pages, 6 figures, accepted for publication in A&A (updated to
match proofs
Towards Cancer Hybrid Automata
This paper introduces Cancer Hybrid Automata (CHAs), a formalism to model the
progression of cancers through discrete phenotypes. The classification of
cancer progression using discrete states like stages and hallmarks has become
common in the biology literature, but primarily as an organizing principle, and
not as an executable formalism. The precise computational model developed here
aims to exploit this untapped potential, namely, through automatic verification
of progression models (e.g., consistency, causal connections, etc.),
classification of unreachable or unstable states and computer-generated
(individualized or universal) therapy plans. The paper builds on a
phenomenological approach, and as such does not need to assume a model for the
biochemistry of the underlying natural progression. Rather, it abstractly
models transition timings between states as well as the effects of drugs and
clinical tests, and thus allows formalization of temporal statements about the
progression as well as notions of timed therapies. The model proposed here is
ultimately based on hybrid automata, and we show how existing controller
synthesis algorithms can be generalized to CHA models, so that therapies can be
generated automatically. Throughout this paper we use cancer hallmarks to
represent the discrete states through which cancer progresses, but other
notions of discretely or continuously varying state formalisms could also be
used to derive similar therapies.Comment: In Proceedings HSB 2012, arXiv:1208.315
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