TY  - CHAP
A1  - Curzon, Paul
A1  - Kalas, Ivan
A1  - Schubert, Sigrid
A1  - Schaper, Niclas
A1  - Barnes, Jan
A1  - Kennewell, Steve
A1  - Bröker, Kathrin
A1  - Kastens, Uwe
A1  - Magenheim, Johannes
A1  - Dagiene, Valentina
A1  - Stupuriene, Gabriele
A1  - Ellis, Jason Brent
A1  - Abreu-Ellis, Carla Reis
A1  - Grillenberger, Andreas
A1  - Romeike, Ralf
A1  - Haugsbakken, Halvdan
A1  - Jones, Anthony
A1  - Lewin, Cathy
A1  - McNicol, Sarah
A1  - Nelles, Wolfgang
A1  - Neugebauer, Jonas
A1  - Ohrndorf, Laura
A1  - Schaper, Niclas
A1  - Schubert, Sigrid
A1  - Opel, Simone
A1  - Kramer, Matthias
A1  - Trommen, Michael
A1  - Pottbäcker, Florian
A1  - Ilaghef, Youssef
A1  - Passig, David
A1  - Tzuriel, David
A1  - Kedmi, Ganit Eshel
A1  - Saito, Toshinori
A1  - Webb, Mary
A1  - Weigend, Michael
A1  - Bottino, Rosa
A1  - Chioccariello, Augusto
A1  - Christensen, Rhonda
A1  - Knezek, Gerald
A1  - Gioko, Anthony Maina
A1  - Angondi, Enos Kiforo
A1  - Waga, Rosemary
A1  - Ohrndorf, Laura
A1  - Or-Bach, Rachel
A1  - Preston, Christina
A1  - Younie, Sarah
A1  - Przybylla, Mareen
A1  - Romeike, Ralf
A1  - Reynolds, Nicholas
A1  - Swainston, Andrew
A1  - Bendrups, Faye
A1  - Sysło, Maciej M.
A1  - Kwiatkowska, Anna Beata
A1  - Zieris, Holger
A1  - Gerstberger, Herbert
A1  - Müller, Wolfgang
A1  - Büchner, Steffen
A1  - Opel, Simone
A1  - Schiller, Thomas
A1  - Wegner, Christian
A1  - Zender, Raphael
A1  - Lucke, Ulrike
A1  - Diethelm, Ira
A1  - Syrbe, Jörn
A1  - Lai, Kwok-Wing
A1  - Davis, Niki
A1  - Eickelmann, Birgit
A1  - Erstad, Ola
A1  - Fisser, Petra
A1  - Gibson, David
A1  - Khaddage, Ferial
A1  - Knezek, Gerald
A1  - Micheuz, Peter
A1  - Kloos, Carlos Delgado
ED  - Brinda, Torsten
ED  - Reynolds, Nicholas
ED  - Romeike, Ralf
ED  - Schwill, Andreas
T1  - KEYCIT 2014
BT  - key competencies in informatics and ICT
N2  - In our rapidly changing world it is increasingly important not only to be an expert in a chosen field of study but also to be able to respond to developments, master new approaches to solving problems, and fulfil changing requirements in the modern world and in the job market. In response to these needs key competencies in understanding, developing and using new digital technologies are being brought into focus in school and university programmes. The IFIP TC3 conference "KEYCIT – Key Competences in Informatics and ICT (KEYCIT 2014)" was held at the University of Potsdam in Germany from July 1st to 4th, 2014 and addressed the combination of key competencies, Informatics and ICT in detail. The conference was organized into strands focusing on secondary education, university education and teacher education (organized by IFIP WGs 3.1 and 3.3) and provided a forum to present and to discuss research, case studies, positions, and national perspectives in this field.
T3  - Commentarii informaticae didacticae (CID) - 7 
KW  - Schlüsselkompetenzen
KW  - Informatik
KW  - Bildung
KW  - ICT
KW  - Informatikdidaktik
KW  - Key Competencies
KW  - Informatics
KW  - education
KW  - ICT
KW  - Computer Science Education
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-70325
SN  - 978-3-86956-292-6
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - CHAP
A1  - Arlettaz, Jordane
A1  - Badó, Attila
A1  - Bakos-Kovács, Kitti
A1  - Bató, Szilvia
A1  - Bóka, János
A1  - Congnard, Laureline
A1  - Csatlós, Erzsébet
A1  - Gedeon, Magdolna
A1  - Guemar, Carine
A1  - Hajdú, Dóra
A1  - Jacsó, Judit
A1  - Kelemen, Katalin
A1  - Fekete, Balázs
A1  - Kruzslicz, Péter
A1  - Mezei, Péter
A1  - Szűcs, Tünde
A1  - Zoltán, Péteri
A1  - Szabó, Béla P.
ED  - Badó, Attila
ED  - Belling, Detlev W.
ED  - Bóka, János
ED  - Mezei, Péter
T1  - Internationale Konferenz zum zehnjährigen Bestehen des Instituts für Rechtsvergleichung der Universität Szeged
T1  - International conference for the 10th anniversary of the Institute of Comparative Law of the University of Szeged
T1  - Conférence internationale au 10ème anniversaire de l‘Institut de droit comparé de l‘Université de Szeged
N2  - Die Konferenz „International Conference for the 10th Anniversary of the Institute of Comparative Law” hat am 24. Mai 2013 in Szeged stattgefunden. Im Rahmen der viersprachigen Konferenz haben mehr als dreißig Teilnehmer ihre Forschungsergebnisse präsentiert. Der Essay von Zoltán Péteri blickt auf die Disziplin aus der Perspektive der Wissenschaftsgeschichte. Katalin Kelemen und Balázs Fekete gehen in ihrem Aufsatz der Frage nach, welchen Weg die Versuche der Klassifikation der Rechtssysteme von Osteuropa in der späten Phase der Umbrüche der 1980/90er Jahren genommen haben. Die historische Betrachtungsweise mit Bezug auf Rechtsgeschichte und Rechtsvergleichung spiegelt sich auch in anderen Essays wider, vor allem in den Aufsätzen von Szilvia Bató, Magdolna Gedeon und Béla Szabó P. sowie auch in den Aufsätzen von Péter Mezei und Tünde Szűcs. Attila Badó analysiert die Rechtsvergleichung aus der Sicht des Rechts, der Soziologie und der Politikwissenschaft anhand von Untersuchungen über das Sanktionsystem der Richter in den USA. Diese politikwissenschaftliche Seite wird auch in den Aufsätzen über die aktuellen Fragen der europäischen Integration von Carine Guemar und Laureline Congnard betont. Eine Reihe von Aufsätzen behandeln die konventionelle normative Komparatistik auf dem Gebiet des Verfassungsrechts (Jordane Arlettaz und Péter Kruzslicz), Gesellschaftsrechts (Kitti Bakos-Kovács), Urheberrechts (Dóra Hajdú) und Steuerrechts (Judit Jacsó). Daneben bilden eine weitere Gruppe die Aufsätze von János Bóka und Erzsébet Csatlós, die die Verwendung der vergleichenden Methode in der Praxis der Rechtsprechung untersuchen. Die Rechtsvergleichung ist eine sich dynamisch entwickelnde Disziplin. Die Konferenz und dieser Band dienen nicht nur der Würdigung der bisherigen Arbeit des Instituts für Rechtsvergleichung, sondern zeigen gleichzeitig neue Ziele auf. Die wichtigsten Grundsätze bleiben aber fest verankert auch in einem sich stets verändernden rechtlichen und geistigen Umfeld. Das Motto des Instituts lautet „instruere et docere omnes qui edoceri desiderant“ – „alle lehren, die lernen wollen.“ Auch in den folgenden Jahrzehnten werden uns der Wille des Lernens und Lehrens, die Freiheit der Forschung sowie die Übertragung und Weiterentwicklung der ungarischen wie globalen Rechtskultur leiten.
T3  - Acta Iuridica Universitatis Potsdamiensis - 1 
KW  - Rechtsvergleichung
KW  - Rechtsgeschichte
KW  - Verfassungsrecht
KW  - Gesellschaftrecht
KW  - Urheberrecht
KW  - comparative law
KW  - legal history
KW  - constitutional law
KW  - company law
KW  - copyright law
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-72039
SN  - 978-3-86956-308-4
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - CHAP
A1  - Hofuku, Yayoi
A1  - Cho, Shinya
A1  - Nishida, Tomohiro
A1  - Kanemune, Susumu
A1  - Linck, Barbara
A1  - Kim, Seungyon
A1  - Park, Seongbin
A1  - Vaníček, Jiří
A1  - Gujberová, Monika
A1  - Tomcsányi, Peter
A1  - Dagiene, Valentina
A1  - Jevsikova, Tatjana
A1  - Schulte, Carsten
A1  - Sentance, Sue
A1  - Thota, Neena
A1  - Gülbahar, Yasemin
A1  - İlkhan, Mustafa
A1  - Kilis, Selcan
A1  - Arslan, Okan
A1  - Nakano, Yoshiaki
A1  - Izutsu, Katsunobu
A1  - Lessner, Daniel
A1  - Reffay, Christophe
A1  - Miled, Mahdi
A1  - Ortiz, Pascal
A1  - Février, Loïc
A1  - Grgurina, Nataša
A1  - Weise, Martin
A1  - Bellettini, Carlo
A1  - Lonati, Violetta
A1  - Malchiodi, Dario
A1  - Monga, Mattia
A1  - Morpurgo, Anna
A1  - Torelli, Mauro
A1  - Planteu, Lukas
A1  - Standl, Bernhard
A1  - Grossmann, Wilfried
A1  - Neuwirth, Erich
A1  - Benacka, Jan
A1  - Ragonis, Noa
A1  - Hodges, Steve
A1  - Berry, Carol
A1  - Kusterer, Peter
ED  - Diethelm, Ira
ED  - Arndt, Jannik
ED  - Dünnebier, Malte
ED  - Syrbe, Jörn
T1  - Informatics in schools : local proceedings of the 6th International Conference ISSEP 2013 ; selected papers ; Oldenburg, Germany, February 26–March 2, 2013
N2  - The International Conference on Informatics in Schools: Situation, Evolution and Perspectives – ISSEP – is a forum for researchers and practitioners in the area of Informatics education, both in primary and secondary schools. It provides an opportunity for educators to reflect upon the goals and objectives of this subject, its curricula and various teaching/learning paradigms and topics, possible connections to everyday life and various ways of establishing Informatics Education in schools. This conference also cares about teaching/learning materials, various forms of assessment, traditional and innovative educational research designs, Informatics’ contribution to the preparation of children for the 21st century, motivating competitions, projects and activities supporting informatics education in school.
T3  - Commentarii informaticae didacticae (CID) - 6 
KW  - ISSEP
KW  - Informatics Education
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-63688
SN  - 978-3-86956-222-3
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - CHAP
A1  - Wedernikov, Nikolaij T.
A1  - Sliva, Anatolij J.
A1  - Ebseev, Boris S.
A1  - Mitjukov, Mitjukov, Michail Alekseevič
A1  - Bobrowa, Vera K.
A1  - Yustus, Ekaterina
A1  - Postier, Rüdiger
A1  - Schulze, Carola
A1  - Hoof, Karsten
A1  - Steinhorst, Lars
A1  - Straschun, Boris A.
A1  - Narutto, Svetlana Vasil'evna
A1  - Michaleva, Nadezda A.
A1  - Fadeev, Vladimir Ivanovič
A1  - Warlen, Maria V.
ED  - Schulze, Carola
ED  - Fadeev, Vladimir Ivanovič
T1  - Verfassungsgerichtsbarkeit in der Russischen Föderation und in der Bundesrepublik Deutschland
BT  - Rundtischgespräch an der Moskauer Staatlichen Juristischen Kutafin-Universität am 9. und 10. Oktober 2012
N2  - Der Tagungsband enthält die Referate und Diskussionsbeiträge des in Moskau an der Staatlichen Juristischen Kutafin-Universität am 9. und 10. Oktober 2012 durchgeführten Rundtischgespräches zur Verfassungsgerichtsbarkeit. Behandelt werden ausgewählte rechtshistorische und -politische Fragen sowie aktuelle rechtliche Probleme der Verfassungsgerichtsbarkeit in der Russischen Föderation und der Bundesrepublik Deutschland sowohl aus der Sicht der Rechtspraxis als auch der Wissenschaft: insbesondere die Entwicklung der Verfassungsgerichtsbarkeit in Geschichte und Gegenwart, Status, Rechtsnatur und Aufgaben des Verfassungsgerichts in den Subjekten der Föderation und in den Ländern sowie Verfassungsgericht und Gesetzgebung. Zudem werden Spezialfragen der Verfassungsgerichtsbarkeit erörtert, z.B. die Institution des Bevollmächtigten Vertreters des Präsidenten im Verfassungsgericht in Russland, der Eilrechtsschutz durch das BVerfG und der Rechtsschutz bei überlangen Verfahren vor dem BVerfG in Deutschland.
KW  - Verfassungsgerichtsbarkeit
KW  - Verfassungsgericht
KW  - Status und Aufgaben des Verfassungsgerichts
KW  - verfassungsgerichtliche Kontrolle
Y1  - 2013
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-67861
SN  - 978-3-86956-267-4
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - CHAP
A1  - Banda, Gourinath
A1  - Gallagher, John P.
T1  - Constraint-based abstraction of a model checker for infinite state systems
N2  - Abstract interpretation-based model checking provides an approach to verifying properties of infinite-state systems. In practice, most previous work on abstract model checking is either restricted to verifying universal properties, or develops special techniques for temporal logics such as modal transition systems or other dual transition systems. By contrast we apply completely standard techniques for constructing abstract interpretations to the abstraction of a CTL semantic function, without restricting the kind of properties that can be verified. Furthermore we show that this leads directly to implementation of abstract model checking algorithms for abstract domains based on constraints, making use of an SMT solver.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41516
ER  - 
TY  - CHAP
A1  - Goltz, Hans-Joachim
A1  - Pieth, Norbert
T1  - A tool for generating partition schedules of multiprocessor systems
N2  - A deterministic cycle scheduling of partitions at the operating system level is supposed for a multiprocessor system. In this paper, we propose a tool for generating such schedules. We use constraint based programming and develop methods and concepts for a combined interactive and automatic partition scheduling system. This paper is also devoted to basic methods and techniques for modeling and solving this partition scheduling problem. Initial application of our partition scheduling tool has proved successful and demonstrated the suitability of the methods used.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41556
ER  - 
TY  - CHAP
A1  - Schrijvers, Tom
T1  - Overview of the monadic constraint programming framework
N2  - A constraint programming system combines two essential components: a constraint solver and a search engine. The constraint solver reasons about satisfiability of conjunctions of constraints, and the search engine controls the search for solutions by iteratively exploring a disjunctive search tree defined by the constraint program. The Monadic Constraint Programming framework gives a monadic definition of constraint programming where the solver is defined as a monad threaded through the monadic search tree. Search and search strategies can then be defined as firstclass objects that can themselves be built or extended by composable search transformers. Search transformers give a powerful and unifying approach to viewing search in constraint programming, and the resulting constraint programming system is first class and extremely flexible.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41411
ER  - 
TY  - CHAP
A1  - Herre, Heinrich
A1  - Hummel, Axel
T1  - Stationary generated models of generalized logic programs
N2  - The interest in extensions of the logic programming paradigm beyond the class of normal logic programs is motivated by the need of an adequate representation and processing of knowledge. One of the most difficult problems in this area is to find an adequate declarative semantics for logic programs. In the present paper a general preference criterion is proposed that selects the ‘intended’ partial models of generalized logic programs which is a conservative extension of the stationary semantics for normal logic programs of [Prz91]. The presented preference criterion defines a partial model of a generalized logic program as intended if it is generated by a stationary chain. It turns out that the stationary generated models coincide with the stationary models on the class of normal logic programs. The general wellfounded semantics of such a program is defined as the set-theoretical intersection of its stationary generated models. For normal logic programs the general wellfounded semantics equals the wellfounded semantics.
KW  - extensions of logic programs
KW  - semantics
KW  - knowledge representation
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41501
ER  - 
TY  - CHAP
A1  - Abdennadher, Slim
A1  - Ismail, Haythem
A1  - Khoury, Frederick
T1  - Transforming imperative algorithms to constraint handling rules
N2  - Different properties of programs, implemented in Constraint Handling Rules (CHR), have already been investigated. Proving these properties in CHR is fairly simpler than proving them in any type of imperative programming language, which triggered the proposal of a methodology to map imperative programs into equivalent CHR. The equivalence of both programs implies that if a property is satisfied for one, then it is satisfied for the other. The mapping methodology could be put to other beneficial uses. One such use is the automatic generation of global constraints, at an attempt to demonstrate the benefits of having a rule-based implementation for constraint solvers.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41533
ER  - 
TY  - CHAP
A1  - Betz, Hariolf
A1  - Raiser, Frank
A1  - Frühwirth, Thom
T1  - Persistent constraints in constraint handling rules
N2  - In the most abstract definition of its operational semantics, the declarative and concurrent programming language CHR is trivially non-terminating for a significant class of programs. Common refinements of this definition, in closing the gap to real-world implementations, compromise on declarativity and/or concurrency. Building on recent work and the notion of persistent constraints, we introduce an operational semantics avoiding trivial non-termination without compromising on its essential features.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41547
ER  - 
TY  - CHAP
A1  - Gebser, Martin
A1  - Hinrichs, Henrik
A1  - Schaub, Torsten H.
A1  - Thiele, Sven
T1  - xpanda: a (simple) preprocessor for adding multi-valued propositions to ASP
N2  - We introduce a simple approach extending the input language of Answer Set Programming (ASP) systems by multi-valued propositions. Our approach is implemented as a (prototypical) preprocessor translating logic programs with multi-valued propositions into logic programs with Boolean propositions only. Our translation is modular and heavily benefits from the expressive input language of ASP. The resulting approach, along with its implementation, allows for solving interesting constraint satisfaction problems in ASP, showing a good performance.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41466
ER  - 
TY  - CHAP
A1  - Oetsch, Johannes
A1  - Schwengerer, Martin
A1  - Tompits, Hans
T1  - Kato: a plagiarism-detection tool for answer-set programs
N2  - We present the tool Kato which is, to the best of our knowledge, the first tool for plagiarism detection that is directly tailored for answer-set programming (ASP). Kato aims at finding similarities between (segments of) logic programs to help detecting cases of plagiarism. Currently, the tool is realised for DLV programs but it is designed to handle various logic-programming syntax versions. We review basic features and the underlying methodology of the tool.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41485
ER  - 
TY  - CHAP
A1  - Zhou, Neng-Fa
T1  - What I have learned from all these solver competitions
N2  - In this talk, I would like to share my experiences gained from participating in four CSP solver competitions and the second ASP solver competition. In particular, I’ll talk about how various programming techniques can make huge differences in solving some of the benchmark problems used in the competitions. These techniques include global constraints, table constraints, and problem-specific propagators and labeling strategies for selecting variables and values. I’ll present these techniques with experimental results from B-Prolog and other CLP(FD) systems.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41431
ER  - 
TY  - CHAP
A1  - Hanus, Michael
A1  - Koschnicke, Sven
T1  - An ER-based framework for declarative web programming
N2  - We describe a framework to support the implementation of web-based systems to manipulate data stored in relational databases. Since the conceptual model of a relational database is often specified as an entity-relationship (ER) model, we propose to use the ER model to generate a complete implementation in the declarative programming language Curry. This implementation contains operations to create and manipulate entities of the data model, supports authentication, authorization, session handling, and the composition of individual operations to user processes. Furthermore and most important, the implementation ensures the consistency of the database w.r.t. the data dependencies specified in the ER model, i.e., updates initiated by the user cannot lead to an inconsistent state of the database. In order to generate a high-level declarative implementation that can be easily adapted to individual customer requirements, the framework exploits previous works on declarative database programming and web user interface construction in Curry.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41447
ER  - 
TY  - CHAP
A1  - Geske, Ulrich
A1  - Wolf, Armin
T1  - Preface
N2  - The workshops on (constraint) logic programming (WLP) are the annual meeting of the Society of Logic Programming (GLP e.V.) and bring together researchers interested in logic programming, constraint programming, and related areas like databases, artificial intelligence and operations research. In this decade, previous workshops took place in Dresden (2008), Würzburg (2007), Vienna (2006), Ulm (2005), Potsdam (2004), Dresden (2002), Kiel (2001), and Würzburg (2000). Contributions to workshops deal with all theoretical, experimental, and application aspects of constraint programming (CP) and logic programming (LP), including foundations of constraint/ logic programming. Some of the special topics are constraint solving and optimization, extensions of functional logic programming, deductive databases, data mining, nonmonotonic reasoning, , interaction of CP/LP with other formalisms like agents, XML, JAVA, program analysis, program transformation, program verification, meta programming, parallelism and concurrency, answer set programming, implementation and software techniques (e.g., types, modularity, design patterns), applications (e.g., in production, environment, education, internet), constraint/logic programming for semantic web systems and applications, reasoning on the semantic web, data modelling for the web, semistructured data, and web query languages.
KW  - Logic Programming
KW  - Constraint Solving
KW  - Logics
KW  - Deduction
KW  - Planing
KW  - Optimization
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41401
ER  - 
TY  - CHAP
A1  - Cabalar, Pedro
T1  - Existential quantifiers in the rule body
N2  - In this paper we consider a simple syntactic extension of Answer Set Programming (ASP) for dealing with (nested) existential quantifiers and double negation in the rule bodies, in a close way to the recent proposal RASPL-1. The semantics for this extension just resorts to Equilibrium Logic (or, equivalently, to the General Theory of Stable Models), which provides a logic-programming interpretation for any arbitrary theory in the syntax of Predicate Calculus. We present a translation of this syntactic class into standard logic programs with variables (either disjunctive or normal, depending on the input rule heads), as those allowed by current ASP solvers. The translation relies on the introduction of auxiliary predicates and the main result shows that it preserves strong equivalence modulo the original signature.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41476
ER  - 
TY  - CHAP
A1  - Herre, Heinrich
A1  - Hummel, Axel
T1  - A paraconsistent semantics for generalized logic programs
N2  - We propose a paraconsistent declarative semantics of possibly inconsistent generalized logic programs which allows for arbitrary formulas in the body and in the head of a rule (i.e. does not depend on the presence of any specific connective, such as negation(-as-failure), nor on any specific syntax of rules). For consistent generalized logic programs this semantics coincides with the stable generated models introduced in [HW97], and for normal logic programs it yields the stable models in the sense of [GL88].
KW  - paraconsistency
KW  - generalized logic programs
KW  - multi-valued logic
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41496
ER  - 
TY  - CHAP
A1  - Seipel, Dietmar
T1  - Practical Applications of Extended Deductive Databases in DATALOG*
N2  - A wide range of additional forward chaining applications could be realized with deductive databases, if their rule formalism, their immediate consequence operator, and their fixpoint iteration process would be more flexible. Deductive databases normally represent knowledge using stratified Datalog programs with default negation. But many practical applications of forward chaining require an extensible set of user–defined built–in predicates. Moreover, they often need function symbols for building complex data structures, and the stratified fixpoint iteration has to be extended by aggregation operations. We present an new language Datalog*, which extends Datalog by stratified meta–predicates (including default negation), function symbols, and user–defined built–in predicates, which are implemented and evaluated top–down in Prolog. All predicates are subject to the same backtracking mechanism. The bottom–up fixpoint iteration can aggregate the derived facts after each iteration based on user–defined Prolog predicates.
KW  - deductive databases
KW  - Prolog
KW  - forward / backward chaining
KW  - bottom–up
KW  - top– down
KW  - built–in predicates
KW  - stratification
KW  - function symbols
KW  - XM
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41457
ER  - 
TY  - CHAP
A1  - Brass, Stefan
T1  - Range restriction for general formulas
N2  - Deductive databases need general formulas in rule bodies, not only conjuctions of literals. This is well known since the work of Lloyd and Topor about extended logic programming. Of course, formulas must be restricted in such a way that they can be effectively evaluated in finite time, and produce only a finite number of new tuples (in each iteration of the TP-operator: the fixpoint can still be infinite). It is also necessary to respect binding restrictions of built-in predicates: many of these predicates can be executed only when certain arguments are ground. Whereas for standard logic programming rules, questions of safety, allowedness, and range-restriction are relatively easy and well understood, the situation for general formulas is a bit more complicated. We give a syntactic analysis of formulas that guarantees the necessary properties.
Y1  - 2010
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-41521
ER  - 
TY  - CHAP
A1  - Piskorski, Jakub
T1  - ExPRESS : extraction pattern recognition engine and specification suite
N2  - The emergence of information extraction (IE) oriented pattern engines has been observed during the last decade. Most of them exploit heavily finite-state devices. This paper introduces ExPRESS – a new extraction pattern engine, whose rules are regular expressions over flat feature structures. The underlying pattern language is a blend of two previously introduced IE oriented pattern formalisms, namely, JAPE, used in the widely known GATE system, and the unificationbased XTDL formalism used in SProUT. A brief and technical overview of ExPRESS, its pattern language and the pool of its native linguistic components is given. Furthermore, the implementation of the grammar interpreter is addressed too.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27227
ER  - 
TY  - CHAP
A1  - Watson, Bruce W.
T1  - Advances in automata implementation techniques (Abstract)
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27094
ER  - 
TY  - CHAP
A1  - Barthélemy, François
T1  - Finite-state compilation of feature structures for two-level morphology
N2  - This paper describes a two-level formalism where feature structures are used in contextual rules. Whereas usual two-level grammars describe rational sets over symbol pairs, this new formalism uses tree structured regular expressions. They allow an explicit and precise definition of the scope of feature structures. A given surface form may be described using several feature structures. Feature unification is expressed in contextual rules using variables, like in a unification grammar. Grammars are compiled in finite state multi-tape transducers.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27120
ER  - 
TY  - CHAP
A1  - Blanc, Olivier
A1  - Constant, Matthieu
A1  - Watrin, Patrick
T1  - Segmentation in super-chunks with a finite-state approach
N2  - Since Harris’ parser in the late 50s, multiword units have been progressively integrated in parsers. Nevertheless, in the most part, they are still restricted to compound words, that are more stable and less numerous. Actually, language is full of semi-fixed expressions that also form basic semantic units: semi-fixed adverbial expressions (e.g. time), collocations. Like compounds, the identification of these structures limits the combinatorial complexity induced by lexical ambiguity. In this paper, we detail an experiment that largely integrates these notions in a finite-state procedure of segmentation into super-chunks, preliminary to a parser.We show that the chunker, developped for French, reaches 92.9% precision and 98.7% recall. Moreover, multiword units realize 36.6% of the attachments within nominal and prepositional phrases.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27133
ER  - 
TY  - CHAP
A1  - Bonfante, Guillaume
A1  - Le Roux, Joseph
T1  - Intersection optimization is NP-complete
N2  - Finite state methods for natural language processing often require the construction and the intersection of several automata. In this paper, we investigate the question of determining the best order in which these intersections should be performed. We take as an example lexical disambiguation in polarity grammars. We show that there is no efficient way to minimize the state complexity of these intersections.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27146
ER  - 
TY  - CHAP
A1  - Daciuk, Jan
T1  - Perfect hashing tree automata
N2  - We present an algorithm that computes a function that assigns consecutive integers to trees recognized by a deterministic, acyclic, finite-state, bottom-up tree automaton. Such function is called minimal perfect hashing. It can be used to identify trees recognized by the automaton. Its value may be seen as an index in some other data structures. We also present an algorithm for inverted hashing.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27163
ER  - 
TY  - CHAP
A1  - Padró, Muntsa
A1  - Padró, Lluís
T1  - ME-CSSR : an extension of CSSR using maximum entropy models
N2  - In this work an extension of CSSR algorithm using Maximum Entropy Models is introduced. Preliminary experiments to perform Named Entity Recognition with this new system are presented.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27210
ER  - 
TY  - CHAP
A1  - Bögel, Tina
A1  - Butt, Miriam
A1  - Hautli, Annette
A1  - Sulger, Sebastian
T1  - Developing a finite-state morphological analyzer for Urdu and Hindi
N2  - We introduce and discuss a number of issues that arise in the process of building a finite-state morphological analyzer for Urdu, in particular issues with potential ambiguity and non-concatenative morphology. Our approach allows for an underlyingly similar treatment of both Urdu and Hindi via a cascade of finite-state transducers that transliterates the very different scripts into a common ASCII transcription system. As this transliteration system is based on the XFST tools that the Urdu/Hindi common morphological analyzer is also implemented in, no compatibility problems arise.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27155
ER  - 
TY  - CHAP
A1  - Yli-Jyrä, Anssi
T1  - Applications of diamonded double negation
N2  - Nested complementation plays an important role in expressing counter- i.e. star-free and first-order definable languages and their hierarchies. In addition, methods that compile phonological rules into finite-state networks use double-nested complementation or “double negation”. This paper reviews how the double-nested complementation extends to a relatively new operation, generalized restriction (GR), coined by the author (Yli-Jyrä and Koskenniemi 2004). This operation encapsulates a double-nested complementation and elimination of a concatenation marker, diamond, whose finite occurrences align concatenations in the arguments of the operation. The paper demonstrates that the GR operation has an interesting potential in expressing regular languages, various kinds of grammars, bimorphisms and relations. This motivates a further study of optimized implementation of the operator.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27109
ER  - 
TY  - CHAP
A1  - Barbaiani, Mădălina
A1  - Cancedda, Nicola
A1  - Dance, Chris
A1  - Fazekas, Szilárd
A1  - Gaál, Tamás
A1  - Gaussier, Éric
T1  - Asymmetric term alignment with selective contiguity constraints by multi-tape automata
N2  - This article describes a HMM-based word-alignment method that can selectively enforce a contiguity constraint. This method has a direct application in the extraction of a bilingual terminological lexicon from a parallel corpus, but can also be used as a preliminary step for the extraction of phrase pairs in a Phrase-Based Statistical Machine Translation system. Contiguous source words composing terms are aligned to contiguous target language words. The HMM is transformed into a Weighted Finite State Transducer (WFST) and contiguity constraints are enforced by specific multi-tape WFSTs. The proposed method is especially suited when basic linguistic resources (morphological analyzer, part-of-speech taggers and term extractors) are available for the source language only.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27115
ER  - 
TY  - CHAP
A1  - Karttunen, Lauri
T1  - New features in PARC finite state toolkits (Abstract)
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27085
ER  - 
TY  - CHAP
A1  - Yli-Jyrä, Anssi
T1  - Transducers from parallel replace rules and modes with generalized lenient composition
N2  - Generalized Two-Level Grammar (GTWOL) provides a new method for compilation of parallel replacement rules into transducers. The current paper identifies the role of generalized lenient composition (GLC) in this method. Thanks to the GLC operation, the compilation method becomes bipartite and easily extendible to capture various application modes. In the light of three notions of obligatoriness, a modification to the compilation method is proposed. We argue that the bipartite design makes implementation of parallel obligatoriness, directionality, length and rank based application modes extremely easy, which is the main result of the paper.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27246
ER  - 
TY  - CHAP
A1  - Saléschus, Dirk
T1  - On resolving long distance dependencies in Russian verbs
N2  - Morphological analyses based on word syntax approaches can encounter difficulties with long distance dependencies. The reason is that in some cases an affix has to have access to the inner structure of the form with which it combines. One solution is the percolation of features from ther inner morphemes to the outer morphemes with some process of feature unification. However, the obstacle of percolation constraints or stipulated features has lead some linguists to argue in favour of other frameworks such as, e.g., realizational morphology or parallel approaches like optimality theory. This paper proposes a linguistic analysis of two long distance dependencies in the morphology of Russian verbs, namely secondary imperfectivization and deverbal nominalization.We show how these processes can be reanalysed as local dependencies. Although finitestate frameworks are not bound by such linguistically motivated considerations, we present an implementation of our analysis as proposed in [1] that does not complicate the grammar or enlarge the network unproportionally.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27235
ER  - 
TY  - CHAP
A1  - Ilarraza, Arantza Díaz de
A1  - Gojenola, Koldo
A1  - Oronoz, Maite
A1  - Otaegi, Maialen
A1  - Alegria, Iñaki
T1  - Syntactic error detection and correction in date expressions using finite-state transducers
N2  - This paper presents a system for the detection and correction of syntactic errors. It combines a robust morphosyntactic analyser and two groups of finite-state transducers specified using the Xerox Finite State Tool (xfst). One of the groups is used for the description of syntactic error patterns while the second one is used for the correction of the detected errors. The system has been tested on a corpus of real texts, containing both correct and incorrect sentences, with good results.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27180
ER  - 
TY  - CHAP
A1  - Fernando, Tim
T1  - Temporal propositions as regular languages
N2  - Temporal propositions are mapped to sets of strings that witness (in a precise sense) the propositions over discrete linear Kripke frames. The strings are collected into regular languages to ensure the decidability of entailments given by inclusions between languages. (Various notions of bounded entailment are shown to be expressible as language inclusions.) The languages unwind computations implicit in the logical (and temporal) connectives via a system of finite-state constraints adapted from finite-state morphology. Applications to Hybrid Logic and non-monotonic inertial reasoning are briefly considered.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27194
ER  - 
TY  - CHAP
A1  - Didakowski, Jörg
T1  - SynCoP : combining syntactic tagging with chunking using weighted finite state transducers
N2  - This paper describes the key aspects of the system SynCoP (Syntactic Constraint Parser) developed at the Berlin-Brandenburgische Akademie der Wissenschaften. The parser allows to combine syntactic tagging and chunking by means of constraint grammar using weighted finite state transducers (WFST). Chunks are interpreted as local dependency structures within syntactic tagging. The linguistic theories are formulated by criteria which are formalized by a semiring; these criteria allow structural preferences and gradual grammaticality. The parser is essentially a cascade of WFSTs. To find the most likely syntactic readings a best-path search is used.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27172
ER  - 
TY  - CHAP
A1  - Zarrieß, Sina
A1  - Seeker, Wolfgang
T1  - Finite-state rule deduction for parsing non-constituent coordination
N2  - In this paper, we present a finite-state approach to constituency and therewith an analysis of coordination phenomena involving so-called non-constituents. We show that non-constituents can be seen as parts of fully-fledged constituents and therefore be coordinated in the same way. We have implemented an algorithm based on finite state automata that generates an LFG grammar assigning valid analyses to non-constituent coordination structures in the German language.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27254
ER  - 
TY  - CHAP
A1  - González, Jorge
A1  - Casacuberta, Francisco
T1  - Phrase-based finite state models
N2  - In the last years, statistical machine translation has already demonstrated its usefulness within a wide variety of translation applications. In this line, phrase-based alignment models have become the reference to follow in order to build competitive systems. Finite state models are always an interesting framework because there are well-known efficient algorithms for their representation and manipulation. This document is a contribution to the evolution of finite state models towards a phrase-based approach. The inference of stochastic transducers that are based on bilingual phrases is carefully analysed from a finite state point of view. Indeed, the algorithmic phenomena that have to be taken into account in order to deal with such phrase-based finite state models when in decoding time are also in-depth detailed.
Y1  - 2008
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-27209
ER  - 
TY  - CHAP
A1  - Reimer, O.
A1  - Aharonian, Felix A.
A1  - Hinton, J.
A1  - Hofmann, W.
A1  - Hoppe, S.
A1  - Raue, M.
A1  - Reimer, A.
T1  - VHE gamma-rays from Westerlund 2 and implications for the inferred energetics
N2  - The H.E.S.S. collaboration recently reported the discovery of VHE γ-ray emission coincident with the young stellar cluster Westerlund 2. This system is known to host a population of hot, massive stars, and, most particularly, the WR binary WR 20a. Particle acceleration to TeV energies in Westerlund 2 can be accomplished in several alternative scenarios, therefore we only discuss energetic constraints based on the total available kinetic energy in the system, the actual mass loss rates of respective cluster members, and implied gamma-ray production from processes such as inverse Compton scattering or neutral pion decay. From the inferred gammaray luminosity of the order of 1035erg/s, implications for the efficiency of converting available kinetic energy into non-thermal radiation associated with stellar winds in the Westerlund 2 cluster are discussed under consideration of either the presence or absence of wind clumping.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18172
ER  - 
TY  - CHAP
A1  - Hirschi, Raphael
T1  - The impact of reduced mass loss rates on the evolution of massive stars
N2  - Mass loss is a very important aspect of the life of massive stars. After briefly reviewing its importance, we discuss the impact of the recently proposed downward revision of mass loss rates due to clumping (difficulty to form Wolf-Rayet stars and production of critically rotating stars). Although a small reduction might be allowed, large reduction factors around ten are disfavoured. We then discuss the possibility of significant mass loss at very low metallicity due to stars reaching break-up velocities and especially due to the metal enrichment of the surface of the star via rotational and convective mixing. This significant mass loss may help the first very massive stars avoid the fate of pair-creation supernova, the chemical signature of which is not observed in extremely metal poor stars. The chemical composition of the very low metallicity winds is very similar to that of the most metal poor star known to date, HE1327-2326 and offer an interesting explanation for the origin of the metals in this star. We also discuss the importance of mass loss in the context of long and soft gamma-ray bursts and pair-creation supernovae. Finally, we would like to stress that mass loss in cooler parts of the HR-diagram (luminous blue variable and yellow and red supergiant stages) are much more uncertain than in the hot part. More work needs to be done in these areas to better constrain the evolution of the most massive stars.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17616
ER  - 
TY  - CHAP
A1  - Fullerton, A. W.
A1  - Massa, D. L.
A1  - Prinja, R. K.
T1  - Revised mass-loss rates for O stars from the Pv resonance line
N2  - The P v λλ1118, 1128 resonance doublet is an extraordinarily useful diagnostic of O-star winds, because it bypasses the traditional problems associated with determining mass-loss rates from UV resonance lines. We discuss critically the assumptions and uncertainties involved with using P v to diagnose mass-loss rates, and conclude that the large discrepancies between massloss rates determined from P v and the rates determined from “density squared” emission processes pose a significant challenge to the “standard model” of hot-star winds. The disparate measurements can be reconciled if the winds of O-type stars are strongly clumped on small spatial scales, which in turn implies that mass-loss rates based on Hα or radio emission are too large by up to an order of magnitude.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17647
ER  - 
TY  - CHAP
A1  - Bouret, J.-C.
A1  - Lanz, T.
A1  - Hillier, D. J.
A1  - Foellmi, C.
T1  - Clumping in O-type Supergiants
N2  - We have analyzed the spectra of seven Galactic O4 supergiants, with the NLTE wind code CMFGEN. For all stars, we have found that clumped wind models match well lines from different species spanning a wavelength range from FUV to optical, and remain consistent with Hα data. We have achieved an excellent match of the P V λλ1118, 1128 resonance doublet and N IV λ1718, as well as He II λ4686 suggesting that our physical description of clumping is adequate. We find very small volume filling factors and that clumping starts deep in the wind, near the sonic point. The most crucial consequence of our analysis is that the mass loss rates of O stars need to be revised downward significantly, by a factor of 3 and more compared to those obtained from smooth-wind models.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17662
ER  - 
TY  - CHAP
A1  - Gull, T. R.
T1  - Eta Carinae viewed from different vantages
N2  - The spatially-resolved winds of the massive binary, Eta Carinae, extend an arcsecond on the sky, well beyond the 10 to 20 milliarcsecond binary orbital dimension. Stellar wind line profiles, observed at very different angular resolutions of VLTI/AMBER, HST/STIS and VLT/UVES, provide spatial information on the extended wind interaction structure as it changes with orbital phase. These same wind lines, observable in the starlight scattered off the foreground lobe of the dusty Homunculus, provide time-variant line profiles viewed from significantly different angles. Comparisons of direct and scattered wind profiles observed in the same epoch and at different orbital phases provide insight on the extended wind structure and promise the potential for three-dimensional imaging of the outer wind structures. Massive, long-lasting clumps, including the nebularWeigelt blobs, originated during the two historical ejection events. Wind interactions with these clumps are quite noticeable in spatially-resolved spectroscopy. As the 2009.0 minimum approaches, analysis of existing spectra and 3-D modeling are providing bases for key observations to gain further understanding of this complex massive binary.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18200
ER  - 
TY  - CHAP
A1  - Reimer, A.
T1  - Clumping effects on non-thermal particle spectra in massive star systems
N2  - Observational evidence exists that winds of massive stars are clumped. Many massive star systems are known as non-thermal particle production sites, as indicated by their synchrotron emission in the radio band. As a consequence they are also considered as candidate sites for non-thermal high-energy photon production up to gamma-ray energies. The present work considers the effects of wind clumpiness expected on the emitting relativistic particle spectrum in colliding wind systems, built up from the pool of thermal wind particles through diffusive particle acceleration, and taking into account inverse Compton and synchrotron losses. In comparison to a homogeneous wind, a clumpy wind causes flux variations of the emitting particle spectrum when the clump enters the wind collision region. It is found that the spectral features associated with this variability moves temporally from low to high energy bands with the time shift between any two spectral bands being dependent on clump size, filling factor, and the energy-dependence of particle energy gains and losses.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18246
ER  - 
TY  - CHAP
A1  - Schnurr, O.
A1  - Crowther, P. A.
T1  - Mid-IR observations of WC stars, and the connection to wind clumping
N2  - We present preliminary results of a tailored atmosphere analysis of six Galactic WC stars using UV, optical, and mid-infrared Spitzer IRS data. With these data, we are able to sample regions from 10 to 10³ stellar radii, thus to determine wind clumping in different parts of the wind. Ultimately, derived wind parameters will be used to accuratelymeasure neon abundances, and to so test predicted nuclear-reaction rates.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17884
ER  - 
TY  - CHAP
A1  - Vink, J. S.
A1  - Benaglia, P.
A1  - Davies, B.
A1  - de Koter, A.
A1  - Oudmaijer, R. D.
T1  - Advances in mass-loss predictions
N2  - We present the results of Monte Carlo mass-loss predictions for massive stars covering a wide range of stellar parameters. We critically test our predictions against a range of observed massloss rates – in light of the recent discussions on wind clumping. We also present a model to compute the clumping-induced polarimetric variability of hot stars and we compare this with observations of Luminous Blue Variables, for which polarimetric variability is larger than for O and Wolf-Rayet stars. Luminous Blue Variables comprise an ideal testbed for studies of wind clumping and wind geometry, as well as for wind strength calculations, and we propose they may be direct supernova progenitors.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17948
ER  - 
TY  - CHAP
A1  - Moffat, Anthony F. J.
A1  - Hillier, D. J.
A1  - Hamann, Wolf-Rainer
A1  - Owocki, S. P.
T1  - General Discussion
N2  - Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17953
ER  - 
TY  - CHAP
A1  - Sonneborn, G.
T1  - Imaging and spectroscopy with the James Webb Space Telescope
N2  - The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope scheduled for launch in 2013. JWST will find the first stars and galaxies that formed in the early universe, connecting the Big Bang to our own Milky Way galaxy. JWST will peer through dusty clouds to see stars forming planetary systems, connecting the MilkyWay to our own Solar System. JWST’s instruments are designed to work primarily in the infrared range of 1 - 28 μm, with some capability in the visible range. JWST will have a large mirror, 6.5 m in diameter, and will be diffraction-limited at 2 μm (0.1 arcsec resolution). JWST will be placed in an L2 orbit about 1.5 million km from the Earth. The instruments will provide imaging, coronography, and multi-object and integral-field spectroscopy across the 1 - 28 μm wavelength range. The breakthrough capabilities of JWST will enable new studies of massive star winds from the Milky Way to the early universe.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17983
ER  - 
TY  - CHAP
A1  - Owocki, S. P.
T1  - Dynamical simulation of the “velocity-porosity” reduction in observed strength of stellar wind lines
N2  - I use dynamical simulations of the line-driven instability to examine the potential role of the resulting flow structure in reducing the observed strength of wind absorption lines. Instead of the porosity length formalism used to model effects on continuum absorption, I suggest reductions in line strength can be better characterized in terms of a velocity clumping factor that is insensitive to spatial scales. Examples of dynamic spectra computed directly from instability simulations do exhibit a net reduction in absorption, but only at a modest 10-20% level that is well short of the ca. factor 10 required by recent analyses of PV lines.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17992
ER  - 
TY  - CHAP
A1  - Blomme, R.
T1  - Corotating Interaction Regions and clumping
N2  - We present hydrodynamical models for Corotating Interaction Regions, which were used by Lobel (2007) to model the Discrete Absorption Components in HD 64760. We also discuss our failure to model the rotational modulations seen in the same star.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18100
ER  - 
TY  - CHAP
A1  - Kholtygin, A. F.
T1  - Wavelets for looking for clumping in the wind of OB stars
N2  - Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17796
ER  - 
TY  - CHAP
A1  - Urbaneja, M. A.
A1  - Kudritzki, R.-P.
A1  - Puls, Joachim
T1  - Clumping in the winds of O-type CSPNs
N2  - Recent studies of massive O-type stars present clear evidences of inhomogeneous and clumped winds. O-type (H-rich) central stars of planetary nebulae (CSPNs) are in some ways the low mass–low luminosity analogous of those massive stars. In this contribution, we present preliminary results of our on-going multi-wavelength (FUV, UV and optical) study of the winds of Galactic CSPNs. Particular emphasis will be given to the clumping factors derived by means of optical lines (Hα and Heii 4686) and “classic” FUV (and UV) lines.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17801
ER  - 
TY  - CHAP
A1  - de Koter, A.
A1  - Vink, J. S.
A1  - Muijres, L.
T1  - Constraints on wind clumping from the empirical mass-loss vs. metallicity relation for early-type stars
N2  - We present the latest results on the observational dependence of the mass-loss rate in stellar winds of O and early-B stars on the metal content of their atmospheres, and compare these with predictions. Absolute empirical rates for the mass loss of stars brighter than 10$^{5.2} L_{\odot}$, based on H$\alpha$ and ultraviolet (UV) wind lines, are found to be about a factor of two higher than predictions. If this difference is attributed to inhomogeneities in the wind this would imply that luminous O and early-B stars have clumping factors in their H$\alpha$ and UV line forming regime of about a factor of 3--5. The investigated stars cover a metallicity range $Z$ from 0.2 to 1 $Z_{\odot}$. We find a hint towards smaller clumping factors for lower $Z$. The derived clumping factors, however, presuppose that clumping does not impact the predictions of the mass-loss rate. We discuss this assumption and explain how we intend to investigate its validity in more detail.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17736
ER  - 
TY  - CHAP
A1  - Reyes-Iturbide, J.
A1  - Velázquez, P.
A1  - Rosado, M.
T1  - 3D numerical model for an asymmetrical superbubble
N2  - Massive stars usually form groups such as OB associations. Their fast stellar winds sweep up collectively the surrounding insterstellar medium (ISM) to generate superbubbles. Observations suggest that superbubble evolution on the surrounding ISM can be very irregular. Numerical simulations considering these conditions could help to understand the evolution of these superbubbles and to clarify the dynamics of these objects as well as the difference between observed X-ray luminosities and the predicted ones by the standard model (Weaver et al. 1977).
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17724
ER  - 
TY  - CHAP
A1  - Groh, J. H.
A1  - Hillier, D. J.
A1  - Damineli, A.
T1  - Mass-loss rate and clumping in LBV stars : the impact of time-dependent effects
N2  - This paper outlines a newly-developed method to include the effects of time variability in the radiative transfer code CMFGEN. It is shown that the flow timescale is often large compared to the variability timescale of LBVs. Thus, time-dependent effects significantly change the velocity law and density structure of the wind, affecting the derivation of the mass-loss rate, volume filling factor, wind terminal velocity, and luminosity. The results of this work are directly applicable to all active LBVs in the Galaxy and in the LMC, such as AG Car, HR Car, S Dor and R 127, and could result in a revision of stellar and wind parameters. The massloss rate evolution of AG Car during the last 20 years is presented, highlighting the need for time-dependent models to correctly interpret the evolution of LBVs.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17773
ER  - 
TY  - CHAP
ED  - Kurths, Jürgen
ED  - Fradkov, Alexander
ED  - Chen, Guanrong
T1  - The 3rd international IEEE scientific conference on physics and control (PhysCon 2007) : September 3rd-7th 2007 at the University of Potsdam
N2  - During the last few years there was a tremendous growth of scientific activities in the fields related to both Physics and Control theory: nonlinear dynamics, micro- and nanotechnologies, self-organization and complexity, etc. New horizons were opened and new exciting applications emerged. Experts with different backgrounds starting to work together need more opportunities for information exchange to improve mutual understanding and cooperation. The Conference "Physics and Control 2007" is the third international conference focusing on the borderland between Physics and Control with emphasis on both theory and applications. With its 2007 address at Potsdam, Germany, the conference is located for the first time outside of Russia. The major goal of the Conference is to bring together researchers from different scientific communities and to gain some general and unified perspectives in the studies of controlled systems in physics, engineering, chemistry, biology and other natural sciences. We hope that the Conference helps experts in control theory to get acquainted with new interesting problems, and helps experts in physics and related fields to know more about ideas and tools from the modern control theory.
KW  - nonlinear dynamics
KW  - micro- and nanotechnologies
KW  - self-organization
KW  - complexity
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-15228
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - CHAP
A1  - Puls, Joachim
T1  - Discussion : X-rays
N2  - Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18000
ER  - 
TY  - CHAP
A1  - Szeifert, T.
T1  - Wind variabilities and asymmetries in Luminous Blue Variables
N2  - Luminous Blue Variables show strong changes in their stellar wind on time scales of typically years to decades when they expand and contract radially at approximately constant luminosity. Micro-variability on shorter time scales and amplitudes can be observed superimposed to the larger scale radial changes. I will show long-term time series of high resolution spectra which we have collected in the past 20 years for many of the well known LBVs together with a few time series of weekly sampling (HR Car, R40, R71, R110, R127, S Dor) covering a time windows of up to a few months. Wind variability is seen on short and intermediate time scales with the line profiles changing from P Cygni to inverse P Cygni and double peeked profiles sometimes for the same star and spectral line. On longer time scales the ionisation levels for all chemical elements change drastically due to the strong change of the temperature on the stellar surface. While on the long term the characteristic radial changes may have impact on the over all mass loss rates, the variabilities and asymmetries on short and intermediate time scales may cause false estimates of the mass loss rates when confronting models with the observed line profiles
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18146
ER  - 
TY  - CHAP
A1  - Moffat, Anthony F. J.
T1  - Observational overview of clumping in hot stellar winds
N2  - In the old days (pre ∼1990) hot stellar winds were assumed to be smooth, which made life fairly easy and bothered no one. Then after suspicious behaviour had been revealed, e.g. stochastic temporal variability in broadband polarimetry of single hot stars, it took the emerging CCD technology developed in the preceding decades (∼1970-80’s) to reveal that these winds were far from smooth. It was mainly high-S/N, time-dependent spectroscopy of strong optical recombination emission lines in WR, and also a few OB and other stars with strong hot winds, that indicated all hot stellar winds likely to be pervaded by thousands of multiscale (compressible supersonic turbulent?) structures, whose driver is probably some kind of radiative instability. Quantitative estimates of clumping-independent mass-loss rates came from various fronts, mainly dependent directly on density (e.g. electron-scattering wings of emission lines, UV spectroscopy of weak resonance lines, and binary-star properties including orbital-period changes, electron-scattering, and X-ray fluxes from colliding winds) rather than the more common, easier-to-obtain but clumping-dependent density-squared diagnostics (e.g. free-free emission in the IR/radio and recombination lines, of which the favourite has always been Hα). Many big questions still remain, such as: What do the clumps really look like? Do clumping properties change as one recedes from the mother star? Is clumping universal? Does the relative clumping correction depend on $\dot{M}$ itself?
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17633
ER  - 
TY  - CHAP
A1  - Puls, Joachim
A1  - Markova, N.
A1  - Najarro, F.
A1  - Hanson, M. M.
T1  - Clumping in O-star winds
N2  - We review various diagnostics of clumping in O-star winds, with special emphasis on its radial stratification. Implications and problems are discussed, and promising NIR methods are presented.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17683
ER  - 
TY  - CHAP
A1  - St-Louis, N.
A1  - Moffat, Anthony F. J.
T1  - Do clumping corrections increase with decreasing mass-loss rates?
N2  - We report on new mass-loss rate estimates for O stars in six massive binaries using the amplitude of orbital-phase dependent, linear-polarimetric variability caused by electron scattering off free electrons in the winds. Our estimated mass-loss rates for luminous O stars are independent of clumping. They suggest similar clumping corrections as for WR stars and do not support the recently proposed reduction in mass-loss rates of O stars by one or two orders of magnitude.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17696
ER  - 
TY  - CHAP
A1  - Smith, Nathan
T1  - Independent signs of lower mass-loss rates for O-type stars
N2  - I discuss observational evidence – independent of the direct spectral diagnostics of stellar winds themselves – suggesting that mass-loss rates for O stars need to be revised downward by roughly a factor of three or more, in line with recent observed mass-loss rates for clumped winds. These independent constraints include the large observed mass-loss rates in LBV eruptions, the large masses of evolved massive stars like LBVs and WNH stars, WR stars in lower metallicity environments, observed rotation rates of massive stars at different metallicity, supernovae that seem to defy expectations of high mass-loss rates in stellar evolution, and other clues. I pay particular attention to the role of feedback that would result from higher mass-loss rates, driving the star to the Eddington limit too soon, and therefore making higher rates appear highly implausible. Some of these arguments by themselves may have more than one interpretation, but together they paint a consistent picture that steady line-driven winds of O-type stars have lower mass-loss rates and are significantly clumped.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17659
ER  - 
TY  - CHAP
A1  - Votruba, V.
A1  - Feldmeier, Achim
A1  - Kubát, Jiří
A1  - Rätzel, D.
T1  - Multicomponent stellar wind of hot stars
N2  - We developed a time-dependent multicomponent hydrodynamical code for simulation of the stellar wind from hot stars and applied it to stars with high and low density winds.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17677
ER  - 
TY  - CHAP
A1  - Lobel, A.
T1  - Modeling DACs in UV lines of massive hot stars
N2  - We apply the 3-dimensional radiative transport codeWind3D to 3D hydrodynamic models of Corotating Interaction Regions to fit the detailed variability of Discrete Absorption Components observed in Si iv UV resonance lines of HD 64760 (B0.5 Ib). We discuss important effects of the hydrodynamic input parameters on these large-scale equatorial wind structures that determine the detailed morphology of the DACs computed with 3D transfer. The best fit model reveals that the CIR in HD 64760 is produced by a source at the base of the wind that lags behind the stellar surface rotation. The non-corotating coherent wind structure is an extended density wave produced by a local increase of only 0.6% in the smooth symmetric wind mass-loss rate.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17856
ER  - 
TY  - CHAP
A1  - Prinja, R. K.
A1  - Hodges, S. E.
A1  - Massa, D. L.
A1  - Fullerton, A. W.
A1  - Burnley, A. W.
T1  - Structure in the fast wind of NGC6543
N2  - We exploit time-series $FUSE$ spectroscopy to {\it uniquely} probe spatial structure and clumping in the fast wind of the central star of the H-rich planetary nebula NGC~6543 (HD~164963). Episodic and recurrent optical depth enhancements are discovered in the P{\sc v} absorption troughs, with some evidence for a $\sim$ 0.17-day modulation time-scale. The characteristics of these features are essentially identical to the discrete absorption components' (DACs) commonly seen in the UV lines of massive OB stars, suggesting the temporal structures seen in NGC~6543 likely have a physical origin that is similar to that operating in massive, luminous stars. The mechanism for forming coherent perturbations in the outflows is therefore apparently operating equally in the radiation-pressure-driven winds of widely differing momenta ($\mdot$$v_\infty$$R_\star^{0.5}$) and flow times, as represented by OB stars and CSPN.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17788
ER  - 
TY  - CHAP
A1  - Marchenko, S. V.
T1  - Wind inhomogeneities in low-Z environment : observations
N2  - We discuss the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is $\sim 1/5 Z_\odot$. We were able to detect and follow numerous small-scale wind-embedded inhomogeneities in all observed stars. The general properties of the moving features, such as their velocity dispersions, emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17769
ER  - 
TY  - CHAP
A1  - Najarro, F.
A1  - Puls, Joachim
A1  - Herrero, A.
A1  - Hanson, M. M.
A1  - Martín-Pintado, J.
A1  - Hillier, D. J.
T1  - Tracking the Clumping in OB Stars from UV to radio
N2  - We review different line and continua diagnostics from the UV to radio, which can be utilized to simultaneously constrain the clumping structure throughout the stellar wind of massive OB stars.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17701
ER  - 
TY  - CHAP
A1  - Massa, D. L.
T1  - Discussion: Spectroscopy and Mass-Loss Diagnostics
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17821
ER  - 
TY  - CHAP
A1  - Liermann, A.
A1  - Hamann, Wolf-Rainer
T1  - Clumping in Galactic WN stars : a comparison of mass loss rates from UV/optical & radio diagnostics
N2  - The mass loss rates and other parameters for a large sample of Galactic WN stars have been revised by Hamann et al. (2006), using the most up-to date Potsdam Wolf-Rayet (PoWR) model atmospheres. For a sub-sample of these stars exist measurements of their radio free-free emission. After harmonizing the adopted distance and terminal wind velocities, we compare the mass loss rates obtained from the two diagnostics. The differences are discussed as a possible consequence of different clumping contrast in the line-forming and radio-emitting regions.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17816
ER  - 
TY  - CHAP
A1  - Raassen, A. J. J.
A1  - Hucht, K. A. van der
A1  - Miller, N. A.
A1  - Cassinelli, Joseph P.
T1  - XMM-Newton observations of zeta Orionis (O9.7 Ib) : a collisional ionization equilibrium model
N2  - We present the analysis of XMM-Newton observations of ζ Orionis. The analysis is based on fitting to the total spectrum as well as diagnostics of individual line.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17747
ER  - 
TY  - CHAP
A1  - Ignace, R.
A1  - Gayley, K. G.
T1  - Circumstellar Magnetic Field Diagnostics from Line Polarization
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18066
ER  - 
TY  - CHAP
A1  - Walter, R.
A1  - Zurita-Heras, J.
A1  - Leyder, J.-C.
T1  - Probing clumpy stellar winds with a neutron star
N2  - INTEGRAL tripled the number of super-giant high-mass X-ray binaries (sgHMXB) known in the Galaxy by revealing absorbed and fast transient (SFXT) systems. Quantitative constraints on the wind clumping of massive stars can be obtained from the study of the hard X-ray variability of SFXT. A large fraction of the hard X-ray emission is emitted in the form of flares with a typical duration of 3 ksec, frequency of 7 days and luminosity of $10^{36}$ erg/s. Such flares are most probably emitted by the interaction of a compact object orbiting at $\sim10~R_*$ with wind clumps ($10^{22 ... 23}$ g) representing a large fraction of the stellar mass-loss rate. The density ratio between the clumps and the inter-clump medium is $10^{2 ... 4}$. The parameters of the clumps and of the inter-clump medium, derived from the SFXT flaring behavior, are in good agreement with macro-clumping scenario and line-driven instability simulations. SFXT are likely to have larger orbital radius than classical sgHMXB.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18024
ER  - 
TY  - CHAP
A1  - Cassinelli, Joseph P.
A1  - Ignace, R.
A1  - Waldron, W.
A1  - Cho, J.
A1  - Murphy, N.
A1  - Lazarian, A.
T1  - X-ray line emission produced in clump bow shocks
N2  - We summarize Chandra observations of the emission line profiles from 17 OB stars. The lines tend to be broad and unshifted. The forbidden/intercombination line ratios arising from Helium-like ions provide radial distance information for the X-ray emission sources, while the H-like to He-like line ratios provide X-ray temperatures, and thus also source temperature versus radius distributions. OB stars usually show power law differential emission measure distributions versus temperature. In models of bow shocks, we find a power law differential emission measure, a wide range of ion stages, and the bow shock flow around the clumps provides transverse velocities comparable to HWHM values. We find that the bow shock results for the line profile properties, consistent with the observations of X-ray line emission for a broad range of OB star properties.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18057
ER  - 
TY  - CHAP
A1  - Runacres, M. C.
T1  - Hydrodynamical models of clumping beyond 50 R∗
N2  - We present one-dimensional, time-dependent models of the clumps generated by the linedeshadowing instability. In order to follow the clumps out to distances of more than 1000 R∗, we use an efficient moving-box technique. We show that, within the approximations, the wind can remain clumped well into the formation region of the radio continuum.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18030
ER  - 
TY  - CHAP
A1  - Schnerr, R. S.
A1  - Henrichs, H. F.
T1  - Magnetic fields and wind variability in massive stars
N2  - This paper describes the thesis work of Schnerr (2007) entitled ”Magnetic fields and mass loss in massive stars“, which aimed at a better understanding of the impact of magnetic fields on the winds of massive stars.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18075
ER  - 
TY  - CHAP
A1  - Leutenegger, M. A.
A1  - Cohen, David H.
A1  - Kahn, S. M.
A1  - Owocki, S. P.
A1  - Paerels, F. B. S.
T1  - Resonance scattering in the X-ray emission lines profiles of ζ Puppis
N2  - We present XMM-Newton Reflection Grating Spectrometer observations of pairs of X-ray emission line profiles from the O star ζ Pup that originate from the same He-like ion. The two profiles in each pair have different shapes and cannot both be consistently fit by models assuming the same wind parameters. We show that the differences in profile shape can be accounted for in a model including the effects of resonance scattering, which affects the resonance line in the pair but not the intercombination line. This implies that resonance scattering is also important in single resonance lines, where its effect is difficult to distinguish from a low effective continuum optical depth in the wind. Thus, resonance scattering may help reconcile X-ray line profile shapes with literature mass-loss rates.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18085
ER  - 
TY  - CHAP
A1  - Massa, D. L.
A1  - Prinja, R. K.
A1  - Fullerton, A. W.
T1  - The effects of clumping on wind line variability
N2  - We review the effects of clumping on the profiles of resonance doublets. By allowing the ratio of the doublet oscillator strenghts to be a free parameter, we demonstrate that doublet profiles contain more information than is normally utilized. In clumped (or porous) winds, this ratio can lies between unity and the ratio of the f-values, and can change as a function of velocity and time, depending on the fraction of the stellar disk that is covered by material moving at a particular velocity at a given moment. Using these insights, we present the results of SEI modeling of a sample of B supergiants, ζ Pup and a time series for a star whose terminal velocity is low enough to make the components of its Si VIλλ1400 independent. These results are interpreted within the framewrok of the Oskinova et al. (2007) model, and demonstrate how the doublet profiles can be used to extract infromation about wind structure.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18095
ER  - 
TY  - CHAP
A1  - Vink, J. S.
T1  - Discussion: Hydrodynamic modeling
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18046
ER  - 
TY  - CHAP
A1  - Hillier, D. J.
T1  - On the influence of clumping on O and Wolf-Rayet spectra
N2  - Overwhelming observational and theoretical evidence suggests that the winds of massive stars are highly clumped. We briefly discuss the influence of clumping on model diagnostics and the difficulties of allowing for the influence of clumping on model spectra. Because of its simplicity, and because of computational ease, most spectroscopic analyses incorporate clumping using the volume filling factor. The biases introduced by this approach are uncertain. To investigate alternative clumping models, and to help determine the validity of parameters derived using the volume filling factor method, we discuss results derived using an alternative model in which we assume that the wind is composed of optically thick shells.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17903
ER  - 
TY  - CHAP
A1  - Fullerton, A. W.
T1  - Discussion: Spectral modeling
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17917
ER  - 
TY  - CHAP
A1  - Townsend, R. H. D.
T1  - Techniques for simulating radiative transfer through porous media
N2  - In this contribution, I discuss some basic techniques that can be used to simulate radiative transfer through porous media. As specific examples, I consider scattering transfer through a clumped slab, and X-ray emission line formation in a clumped wind.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17866
ER  - 
TY  - CHAP
A1  - ud-Doula, A.
T1  - Large-scale wind structure due to magnetic fields
N2  - Magnetic fields influence the dynamics of hot-star winds and create large scale structure. Based on numerical magnetohydrodynamic (MHD) simulations, we model the wind of θ¹ Ori C, and then use the SEI method to compute synthetic line profiles for a range of viewing angles as function of rotational phase. The resulting dynamic spectrum for a moderately strong line shows a distinct modulation, but with a phase that seems at odds with available observations.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18010
ER  - 
TY  - CHAP
A1  - Iping, R.C.
A1  - Sonneborn, G.
A1  - Massa, D.L.
A1  - Gies, D.
A1  - Williams, Simon E.
T1  - Far-ultraviolet spectroscopy of O+O binaries in the Magellanic Clouds
N2  - We report FUSE observations in 2005–2006 of three O-type, double-lined spectroscopic binaries in the Magellanic Clouds. The systems have very short periods (1.4–2.25 d), represent rare, young evolutionary stages of massive stars and binaries, and provide a unique glimpse at some of the most massive systems that form in dense clusters of massive stars. Improved orbit parameters, including revised masses, for LH54-425 are derived from new ctio spectroscopy. The systems are: LH54-425 in the LMC (O3V + O5V, P=2.25d, 62+37M⊙), J053441-693139 in the LMC (O2-3If+O6V, P=1.4 d, 41+27M⊙), and Hodge 53-47 in the SMC (O6V + O4-5IIIf, P=2.2 d, 24+14M⊙, where the O4 star appears to be less massive than the O6 star). Their short periods indicates that wind interaction and mass transfer are likely important factors in their evolution. The spectra provide quantitative and systematic studies of phase-dependent stellar wind properties, wind collision effects in O+O binaries at lower metallicities, improved radial velocity curves, and FUV spectro-photometric changes as a function of orbital phase.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17896
ER  - 
TY  - CHAP
A1  - Kusterer, D.-J.
A1  - Nagel, T.
A1  - Werner, K.
A1  - Feldmeier, Achim
T1  - Radiative transfer in CV disk winds
N2  - Mass accretion onto compact objects through accretion disks is a common phenomenon in the universe. It is seen in all energy domains from active galactic nuclei through cataclysmic variables (CVs) to young stellar objects. Because CVs are fairly easy to observe, they provide an ideal opportunity to study accretion disks in great detail and thus help us to understand accretion also in other energy ranges. Mass accretion in these objects is often accompanied by mass outflow from the disks. This accretion disk wind, at least in CVs, is thought to be radiatively driven, similar to O star winds. WOMPAT, a 3-D Monte Carlo radiative transfer code for accretion disk winds of CVs is presented.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17847
ER  - 
TY  - CHAP
A1  - Davies, B.
A1  - Vink, J. S.
A1  - Oudmaijer, R. D.
T1  - Modelling the polarimetric variability of hot stars
N2  - Many hot stars exhibit stochastic polarimetric variability, thought to arise from clumping low in the wind. Here we investigate the wind properties required to reproduce this variability using analytic models, with particular emphasis on Luminous Blue Variables. We find that the winds must be highly structured, consisting of a large number of optically-thin clumps; while we find that the overall level of polarization should scale with mass-loss rate – consistent with observations of LBVs. The models also predict variability on very short timescales, which is supported by the results of a recent polarimetric monitoring campaign.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17939
ER  - 
TY  - CHAP
A1  - Kubát, Jiří
A1  - Saad, S. M.
T1  - Moving absorption bumps in the spectra of Be stars
N2  - Several Be binaries exhibit an absorption bump moving across the blue wing of hydrogen emission lines towards the line center. This bump is demonstrated for the case of two bright Be stars, κ Dra and 4 Her. It is not clear what is the reason for this travelling bump.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17879
ER  - 
TY  - CHAP
A1  - Nielsen, K. E.
T1  - On irregular line profiles in the optical spectrum of Eta Carinae
N2  - The optical spectrum of Eta Carinae (η Car) is prominent in H I, He i and Fe ii wind lines, all of which vary both in absorption and emission with phase. The phase dependance is a consequence of the interaction between the two objects in the η Car binary (η Car A & B). The binary system is enshrouded by ejecta from previous mass ejection events and consequently, η Car B is not directly observable. We have traced the He i lines over η Car’s spectroscopic period, using HST/STIS data obtained with medium spectral, but high angular, resolving power, and created a radial velocity curve for the system. The He I lines are formed in the core of the system, and appear to be a composite of multiple features formed in spatially separated regions. The sources of their irregular line profiles are still not fully understood, but can be attributed to emission/absorption near the wind-wind interface and/or a direct consequence of the η Car A’s, massive, clumpy wind. This paper will discuss the spectral variability, the narrow emission structure of the He i lines and how clumpiness of the winds may impede the construction of the reliable radial velocity curve, necessary for characterizations of especially η Car B.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18227
ER  - 
TY  - CHAP
A1  - Cohen, David H.
A1  - Leutenegger, M. A.
A1  - Townsend, R. H. D.
T1  - Quantitative analysis of resolved X-ray emission line profiles of O stars
N2  - By quantitatively fitting simple emission line profile models that include both atomic opacity and porosity to the Chandra X-ray spectrum of ζ Pup, we are able to explore the trade-offs between reduced mass-loss rates and wind porosity. We find that reducing the mass-loss rate of ζ Pup by roughly a factor of four, to 1.5 × 10−6 M⊙ yr−1, enables simple non-porous wind models to provide good fits to the data. If, on the other hand, we take the literature mass-loss rate of 6×10−6 M⊙ yr−1, then to produce X-ray line profiles that fit the data, extreme porosity lengths – of h∞ ≈ 3 R∗ – are required. Moreover, these porous models do not provide better fits to the data than the non-porous, low optical depth models. Additionally, such huge porosity lengths do not seem realistic in light of 2-D numerical simulations of the wind instability.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18115
ER  - 
TY  - CHAP
A1  - Morrison, N. D.
A1  - Rother, R.
A1  - Kurschat, N.
T1  - Hα line profile variability in the B8Ia-type supergiant Rigel (β Ori)
N2  - Hα observations of Rigel obtained on 184 nights during the past ten years with the 1-m telescope and ´echelle spectrograph of Ritter Observatory are surveyed. The line profiles were classified in terms of morphology. About 1/4 of them are of P Cygni type, about 15% inverse P Cygni, about 25% double-peaked, about 1/3 pure absorption, and a few are single emission lines. Transformation of the profile from one type to another typically takes a few days. Although the line stays in absorption for extended intervals, only one high-velocity absorption event of the intensity reported by Kaufer et al. (1996a) was observed, in late 2006. Late in this event, Hα absorption occurred farther to the red than the red wing of a plausible photospheric absorption component, an indication of infalling material. In general, as the absorption events come to an end, the emission typically returns with an inverse P Cygni profile. The Hα profile class shows no obvious correlation with the radial velocity of C II λ6578, a photospheric absorption line.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18120
ER  - 
TY  - CHAP
A1  - Chené, A.-N.
A1  - Moffat, Anthony F. J.
A1  - Crowther, P. A.
T1  - Rapidly accelerating clumps in the winds of the very hot WNE Stars
N2  - We study the time variability of emission lines in three WNE stars : WR 2 (WN2), WR 3 (WN3ha) and WR152 (WN3). While WR 2 shows no variability above the noise level, the other stars do show variation, which are like other WR stars in WR 152 but very fast in WR 3. From these motions, we deduce a value of β ∼1 for WR 3 that is like that seen in O stars and β ∼2–3 for WR 152, that is intermediate between other WR stars and WR 3.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18163
ER  - 
TY  - CHAP
A1  - Kholtygin, A. F.
T1  - Modelling the induced clumping stochastic line profile variability
N2  - We model the line profile variability (lpv) in spectra of clumped stellar atmospheres using the Stochastic Clump Model (SCM) of the winds of early-type stars. In this model the formation of dense inhomogeneities (clumps) in the line driven winds is considered as being a stochastic process. It is supposed that the emission due to clumps mainly contributes to the intensities of emission lines in the stellar spectra. It is shown that in the framework of the SCM it is possible to reproduce both the mean line profiles and a common pattern of the lpv.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18180
ER  - 
TY  - CHAP
A1  - Cassinelli, Joseph P.
T1  - Discussion: Magnetic fields, variability
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18195
ER  - 
TY  - CHAP
A1  - St-Louis, N.
T1  - Discussion: Binaries, colliding winds, LBVs and high energy radiation
N2  - Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18155
ER  - 
TY  - CHAP
A1  - Romero, G. E.
A1  - Owocki, S. P.
A1  - Araudo, A. T.
A1  - Townsend, R. H. D.
A1  - Benaglia, P.
T1  - Using gamma-rays to probe the clumped structure of stellar winds
N2  - Gamma-rays can be produced by the interaction of a relativistic jet and the matter of the stellar wind in the subclass of massive X-ray binaries known as “microquasars”. The relativistic jet is ejected from the surroundings of the compact object and interacts with cold protons from the stellar wind, producing pions that then quickly decay into gamma-rays. Since the resulting gamma-ray emissivity depends on the target density, the detection of rapid variability in microquasars with GLAST and the new generation of Cherenkov imaging arrays could be used to probe the clumped structure of the stellar wind. In particular, we show here that the relative fluctuation in gamma rays may scale with the square root of the ratio of porosity length to binary separation, $\sqrt{h/a}$, implying for example a ca. 10% variation in gamma ray emission for a quite moderate porosity, h/a ∼ 0.01.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18210
ER  - 
TY  - CHAP
A1  - Weis, K.
T1  - Wind relics : clumps, inhomogeneities and outflows in LBV nebulae
N2  - The most massive stars are those with the shortest but most active life. One group of massive stars, the Luminous Blue Variables (LBVs), of which only a few objects are known, are in particular of interest concerning the stability of stars. They have a high mass loss rate and are close to being instable. This is even more likely as rotation becomes an important factor in stellar evolution of these stars. Through massive stellar winds and sometimes giant eruptions, LBV nebulae are formed. Various aspects in the evolution in the LBV phase lead, beside the large scale morphological and kinematical differences, to a diversity of small structures like clumps, rims, and outflows in these nebulae.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18235
ER  - 
TY  - CHAP
A1  - Krtička, Jiri
A1  - Puls, Joachim
A1  - Kubát, Jiří
T1  - The influence of clumping on predicted O star wind parameters
N2  - We study the influence of clumping on the predicted wind structure of O-type stars. For this purpose we artificially include clumping into our stationary wind models. When the clumps are assumed to be optically thin, the radiative line force increases compared to corresponding unclumped models, with a similar effect on either the mass-loss rate or the terminal velocity (depending on the onset of clumping). Optically thick clumps, alternatively, might be able to decrease the radiative force.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17969
ER  - 
TY  - CHAP
A1  - Kraus, M.
A1  - Kubát, Jiří
A1  - Krtička, Jiri
T1  - Wind emission of OB supergiants and the influence of clumping
N2  - The influence of the wind to the total continuum of OB supergiants is discussed. For wind velocity distributions with β > 1.0, the wind can have strong influence to the total continuum emission, even at optical wavelengths. Comparing the continuum emission of clumped and unclumped winds, especially for stars with high β values, delivers flux differences of up to 30% with maximum in the near-IR. Continuum observations at these wavelengths are therefore an ideal tool to discriminate between clumped and unclumped winds of OB supergiants.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17757
ER  - 
TY  - CHAP
ED  - Hamann, Wolf-Rainer
ED  - Feldmeier, Achim
ED  - Oskinova, Lida
T1  - Clumping in hot-star winds : proceedings of an international workshop held in Potsdam, Germany, 18. - 22. June 2007
N2  - Stellar winds play an important role for the evolution of massive stars and their cosmic environment. Multiple lines of evidence, coming from spectroscopy, polarimetry, variability, stellar ejecta, and hydrodynamic modeling, suggest that stellar winds are non-stationary and inhomogeneous. This is referred to as 'wind clumping'. The urgent need to understand this phenomenon is boosted by its far-reaching implications. Most importantly, all techniques to derive empirical mass-loss rates are more or less corrupted by wind clumping. Consequently, mass-loss rates are extremely uncertain. Within their range of uncertainty, completely different scenarios for the evolution of massive stars are obtained. Settling these questions for Galactic OB, LBV and Wolf-Rayet stars is prerequisite to understanding stellar clusters and galaxies, or predicting the properties of first-generation stars. In order to develop a consistent picture and understanding of clumped stellar winds, an international workshop on 'Clumping in Hot Star Winds' was held in Potsdam, Germany, from 18. - 22. June 2007. About 60 participants, comprising almost all leading experts in the field, gathered for one week of extensive exchange and discussion. The Scientific Organizing Committee (SOC) included John Brown (Glasgow), Joseph Cassinelli (Madison), Paul Crowther (Sheffield), Alex Fullerton (Baltimore), Wolf-Rainer Hamann (Potsdam, chair), Anthony Moffat (Montreal), Stan Owocki (Newark), and Joachim Puls (Munich). These proceedings contain the invited and contributed talks presented at the workshop, and document the extensive discussions.
KW  - Sternwinde
KW  - Massenverlust
KW  - Strahlungstransport
KW  - hydrodynamische Modellierung
KW  - massereiche Sterne
KW  - stellar winds
KW  - mass loss
KW  - radiative transfer
KW  - hydrodynamic modeling
KW  - massive stars
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13981
SN  - 978-3-940793-33-1
PB  - Universitätsverlag Potsdam
CY  - Potsdam
ER  - 
TY  - CHAP
A1  - Arnold, Gabriele
T1  - Beiträge zur spektralen Fernerkundung fester planetarer Oberflächen
N2  - Dr. Gabriele Arnold ist Leiterin des Bereichs Optische Informationssyteme am Institut für Planetenforschung des Deutschen Zentrums für Luft- und Raumfahrt (DLR) in Berlin-Adlershof  <hr>  Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006
Y1  - 2006
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-7235
N1  - [Poster]
ER  - 
TY  - CHAP
A1  - Doktor, Daniel
A1  - Badeck, Franz-Werner
A1  - Bondeau, Alberte
A1  - Koslowsky, Dirk
A1  - Schaber, Jörg
A1  - McAllister, Murdock
T1  - Using satellite imagery and ground observations to quantify the effect of intra-annually changing temperature patterns on spring time phenology
N2  - Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006
Y1  - 2006
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-7244
N1  - [Poster]
ER  - 
TY  - CHAP
A1  - Domsch, Horst
T1  - Prägnante räumlich-zeitliche Muster einer landwirtschaftlich genutzten Fläche
N2  - In ihrem Bemühen, landwirtschaftliche Flächen standortgerecht zu bewirtschaften, sammelt eine zunehmende Anzahl landwirtschaftlicher Betriebe Informationen über die räumlich-zeitliche Verteilung von Boden- und Pflanzenmerkmalen auf ihren Schlägen. Diese Informationen dienen unmittelbar (Echtzeitansatz) oder mittelbar (Kartenansatz) zur Dosierung von Dünge- und Pflanzenschutzmitteln (Präzise Landbewirtschaftung). Zur Datensammlung werden vorrangig fahrzeuggestützte Sensoren und VIS- und NIR-Luftbilder, aufgenommen aus Sportflugzeugen, verwendet. Erste Betriebe erwerben von Dienstleistungsunternehmen aufbereitete Satelliten-Fernerkundungsdaten. Die landwirtschaftliche und agrartechnische Forschung ist bestrebt, die grundlegenden Muster (z.B. des Ertragspotentials) zu erkennen und damit den Aufwand der Betriebe für eine regelmäßige Informationserfassung gering zu halten.  <hr>  Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006
Y1  - 2006
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-7257
N1  - [Poster]
ER  -