Filtern
Erscheinungsjahr
Dokumenttyp
- Konferenzveröffentlichung (539) (entfernen)
Sprache
- Englisch (456)
- Deutsch (70)
- Mehrsprachig (10)
- Französisch (2)
- Russisch (1)
Schlagworte
- Archiv (4)
- Information Structure (4)
- Nachlass (4)
- Cloud Computing (3)
- E-Learning (3)
- E-Mail Tracking (3)
- ERP (3)
- MOOC (3)
- Privacy (3)
- enterprise systems (3)
- knowledge management (3)
- middleware (3)
- social media (3)
- Blockchain (2)
- COVID-19 (2)
- CPS (2)
- Constraint Solving (2)
- Deduction (2)
- Didaktik (2)
- EMOTIKON (2)
- Forschungsprojekte (2)
- Future SOC Lab (2)
- Hochschuldidaktik (2)
- In-Memory Technologie (2)
- Informatik (2)
- Informatikdidaktik (2)
- Internet of Things (2)
- Interoception (2)
- Linear Mixed Models (2)
- Logic Programming (2)
- Logics (2)
- Multicore Architekturen (2)
- Onlinelehre (2)
- Optimization (2)
- Planing (2)
- Platform Innovation (2)
- Universitätsarchiv (2)
- Verbrechen (2)
- Verfassungsgerichtsbarkeit (2)
- additive particle (2)
- big data (2)
- cloud computing (2)
- conversational agents (2)
- creativity (2)
- crime (2)
- crisis communication (2)
- digital education (2)
- e-learning (2)
- education (2)
- enteprise-level (2)
- evaluation (2)
- higher education (2)
- information systems research (2)
- knowledge transfer (2)
- künstliche Intelligenz (2)
- learning (2)
- machine learning (2)
- maschinelles Lernen (2)
- online course (2)
- online course creation (2)
- online course design (2)
- prediction (2)
- priming (2)
- privacy (2)
- self-disclosure (2)
- "Big Data"-Dienste (1)
- ATLAS.t (1)
- Adipositas (1)
- Alpha-amylase (1)
- Analytic Infrastructures (1)
- Analytics (1)
- Angst (1)
- Aortic valve (1)
- Architekturkonzept (1)
- Aspektorientierte Softwareentwicklung (1)
- Assessment (1)
- Audience Response System (1)
- Ausbildung (1)
- Auswirkungen auf Schüler (1)
- Automatentheorie (1)
- Backgrounding (1)
- Bankenregulierung (1)
- Bankrecht (1)
- Bedürfnisse (1)
- Begnadigung (1)
- Betriebssysteme (1)
- Bildung (1)
- Bildungswissenschaft (1)
- Blood (1)
- Browser Platform (1)
- Browser Platforms (1)
- Bürgerliches Recht (1)
- COCOMO (1)
- Cardiac rehabilitation (1)
- Case Study (1)
- Changing World (1)
- Chrome (1)
- Classroom Response System (1)
- Clicker (1)
- Cloud (1)
- Coccinelle (1)
- Competition (1)
- Compton and pair creation telescope (1)
- Computer Science Education (1)
- Computerlinguistik (1)
- Consensus algorithms (1)
- Construal (1)
- Contrast (1)
- Convergent thinking (1)
- Coring (1)
- Correction (1)
- Countermeasures (1)
- Covid pandemic effects (1)
- Creative process (1)
- Creativity (1)
- Cross-System (1)
- Customization (1)
- Cyber-Phsysische Systeme (1)
- Cyber-Physical Manufacturing Systems (1)
- Dealing with mistakes (1)
- Decentral Decision Making (1)
- Depression (1)
- Developmental gains (1)
- Didaktische Konzepte (1)
- Digital Marketplaces (1)
- Digital Platforms (1)
- Digital-Enabled Human-Information Interaction (1)
- Digitale Bildung (1)
- Discontinued Features (1)
- Diversität (1)
- Drama (1)
- Dynamic Pricing (1)
- EMG (1)
- ERP system (1)
- Echtzeitmessung (1)
- Embodiment (1)
- Emotionen (1)
- Emotions (1)
- Empirical Modelling (1)
- Emulsion (1)
- Endliche Automaten (1)
- Enterprise Resource Planning (1)
- Enterprise Resource Planning (ERP) System (1)
- Enterprise System (1)
- Entwicklung Russlands (1)
- Essstörung (1)
- Euro (1)
- Euro-Financial-Crisis (1)
- Euro-Finanzkrise (1)
- Europa (1)
- Exercise tests (1)
- FORTH (1)
- FabLabs (1)
- Fachdidaktik (1)
- Feature Removal (1)
- Felix-App (1)
- Fiktion (1)
- Finanzmärkte (1)
- Finanzrecht (1)
- Firefox (1)
- Focus (1)
- Focus-sensitivity (1)
- Fokus (1)
- Fokussensitivität (1)
- Folteropfer (1)
- Fontane, Theodor (1)
- Fourier Integraloperatoren (1)
- Game-based learning (1)
- Gamma-ray astronomy (1)
- Gesellschaft (1)
- Gesellschaftrecht (1)
- Gewalt (1)
- Givenness (1)
- Gnade (1)
- Grundrechte (1)
- HDI (1)
- Heart Rate (1)
- Hebbel (1)
- Herodotos (1)
- Heterogenität (1)
- History of pattern occurrences (1)
- Hochschullehre (1)
- Holocaust (1)
- Huguenots (1)
- ICT (1)
- ISSEP (1)
- Impulsivität (1)
- In-Memory technology (1)
- Individualization (1)
- Industrial Analytics (1)
- Industry 4.0 (1)
- Informatics (1)
- Informatics Education (1)
- Informatikstudium (1)
- Information Security and Privacy (1)
- Informationsstruktur (1)
- Innovation in Organizations: Learning (1)
- Instragram (1)
- Integration (1)
- Intentional Forgetting (1)
- Internationale Finanzpolitik (1)
- Internationale Kooperation der Juristischen Fakultät Potsdam (1)
- Ishkashimi (1)
- Justitiabilität (1)
- Key Competencies (1)
- Keyage children (1)
- Kinderpsychologie / Jugendpsychologie / Psychische Störung (1)
- Klimaänderung (1)
- Klinische Psychologie (1)
- Konferenz (1)
- Kongress (1)
- Konstitutionalisierung (1)
- Kreditwesen (1)
- Kriegsopfer (1)
- Krimi (1)
- Kriminalroman (1)
- Kulturmanagement (1)
- Kulturwissenschaften (1)
- Kursdesign (1)
- Kwa languages (1)
- LOGO (1)
- Lagrange Distributionen (1)
- Lagrangian submanifolds (1)
- Landesverfassung (1)
- Langzeitverhalten (1)
- Lean Core (1)
- Learning Analytics (1)
- Lebenslanges Lernen (1)
- Lehramtsstudium (1)
- Lernen (1)
- Liberalisierung (1)
- Life-Long Learning (1)
- Literature Review (1)
- MCT oil (1)
- Machine Learning (1)
- Markedness (1)
- Markov processes (1)
- Markovprozesse (1)
- Massenverlust (1)
- Measuring Efficient Task Processing (1)
- Medialisierung (1)
- Mellin (1)
- Micro Degree (1)
- Middleware (1)
- Migration (1)
- Milk (1)
- Mobile Software Ecosystems (1)
- Mobiles Lernen (1)
- Modeling (1)
- Modification (1)
- Motivation (1)
- Mozilla Firefox (1)
- Mythos (1)
- NMDL (1)
- Narration (1)
- NatRiskChange (1)
- Natural Hazards (1)
- Naturgefahren (1)
- Nazi Germany (1)
- Neurostimulation (1)
- Newsletter (1)
- Older-than-keyage children (1)
- Online Marketing (1)
- Online-Lehre (1)
- Onlinekurs (1)
- Onlinekurs-Produktion (1)
- Optimal Control (1)
- PF Interface (1)
- Papert (1)
- Personal Response System (1)
- Personalization (1)
- Physical Fitness (1)
- Physical fitness (1)
- Platform Coring (1)
- Pockets of creativity (1)
- Point of Care Assay and Vitamin A (1)
- Polonist (1)
- Polonistik (1)
- Pooled Data (1)
- Presse (1)
- Price Cycles (1)
- Primary school children (1)
- Problems (1)
- Process Mining (1)
- Production (1)
- Professionswissen (1)
- Prolog (1)
- Prosody (1)
- Protestantismus (1)
- Prusse (1)
- Pseudo-differential algebras (1)
- RFID (1)
- Raumwirtschaftstheorie (1)
- Reaction Time (1)
- Rechtsgeschichte (1)
- Rechtsvergleichung (1)
- Rechtsvergleichung Russland (1)
- Regionale Untersuchung (1)
- Requirements (1)
- Research Agenda (1)
- Response Strategies (1)
- Romanistik (1)
- Russian History (1)
- Russian Scrambling (1)
- Russian Sign Language (1)
- Russisches Recht (1)
- Russisches Völkerrecht (1)
- Russland (1)
- Salivary (1)
- Sars-CoV-2 (1)
- Schlaf- und Traumforschung (1)
- Schlüsselkompetenzen (1)
- Schulpolitik (1)
- Second World War (1)
- Security (1)
- Sektorale Untersuchung (1)
- Sign Language of the Netherlands (1)
- Slavistik (1)
- Software Platforms (1)
- Soviet History (1)
- Sprachverarbeitung (1)
- Squashes pulp (1)
- Stability (1)
- Status und Aufgaben des Verfassungsgerichts (1)
- Sternwinde (1)
- Strahlungstransport (1)
- Sustainability (1)
- Symposium (1)
- Systematic literature revieew (1)
- Systemsoftware (1)
- TAVI (1)
- Tagung (1)
- Tailoring (1)
- The Sharing Economy (1)
- Three-tier Architecture (1)
- Topic (1)
- Topik (1)
- Tragödie (1)
- Trait Anxiety (1)
- Transcatheter Aortic Valve Implantation (1)
- Transcutaneous Auricular Vagus Nerve Stimulation (1)
- US Intensity (1)
- US Work-up (1)
- UV light (1)
- Umgang mit Fehlern (1)
- Unlearning (1)
- Unternehmens- und Gesellschaftsrecht (1)
- Urheberrecht (1)
- VIL (1)
- Verfassungs- und Staatsangehörigkeitsrecht (1)
- Verfassungsentstehung und -änderung (1)
- Verfassungsgericht (1)
- Verfassungsidentität (1)
- Verfassungsprinzipien (1)
- Verfassungsrecht (1)
- Vermarktung (1)
- Vernetzung Fachwissenschaft (1)
- Verwaltung von Rechenzentren (1)
- Verzweigungsprozesse (1)
- Virtuelle Maschinen (1)
- Woche des Russischen Rechts (1)
- XM (1)
- airbnb (1)
- analytical framework (1)
- argument structure (1)
- artifical intelligence (1)
- artificial intelligence (1)
- artificial neural networks (1)
- aspect adapter (1)
- aspect oriented programming (1)
- aspect-oriented (1)
- aspects (1)
- aspectualization (1)
- attitude-behaviour gap (1)
- augmentation (1)
- automata theory (1)
- backpropagation (1)
- bank regulation (1)
- big data services (1)
- body mass index procedure (1)
- body surface area (1)
- bottom–up (1)
- bracketing paradox (1)
- branching processes (1)
- bug tracking (1)
- built–in predicates (1)
- business models (1)
- business process (1)
- business process optimization (1)
- business process platform (1)
- carotenoids bioavailability (1)
- case study (1)
- case-based reasoning (1)
- certolizumab pegol (1)
- child / adolescent / mental-health problem (1)
- children (1)
- clinical psychology (1)
- clinicians (1)
- co-creation (1)
- cognitive activation (1)
- cognitive levels (1)
- cognitive load theory (1)
- cold pressor pain (1)
- commercialization (1)
- commitment (1)
- company law (1)
- comparative law (1)
- complexity (1)
- computational linguistics (1)
- concurrency (1)
- consistency (1)
- constitutional law (1)
- content knowledge (1)
- contrast (1)
- copyright law (1)
- crime fiction (1)
- crohn's disease (1)
- crosscutting wrappers (1)
- cyber-physical production systems (1)
- cyber-physical systems (1)
- data center management (1)
- data mining (1)
- data security (1)
- data-driven artifacts (1)
- deductive databases (1)
- deep reinforcement learning (1)
- degree of givenness (1)
- deleted tweets (1)
- design-science research (1)
- development in russia (1)
- didactics (1)
- digital identity (1)
- digital platform openness (1)
- digitale Hochschullehre (1)
- digitalization (1)
- dimensional (1)
- discourse referent (1)
- distributed ledger technology (1)
- distributed systems (1)
- documentation (1)
- doubling (1)
- dynamic reconfiguration (1)
- eating disorder (1)
- economic geography (1)
- eference Architecture Model (1)
- effects on pupils (1)
- electromagnetic (1)
- emotion (1)
- empirical evaluation (1)
- engagement (1)
- enhancement (1)
- enterprise architecture (1)
- enterprise ecosystems: the integrated enterprise (1)
- enterprise system (1)
- ethics (1)
- europäische Integration (1)
- experience (1)
- experiment (1)
- explicit knowledge (1)
- extensions of logic programs (1)
- fMRI (1)
- false information (1)
- fat-free mass (1)
- federated industrial platform ecosystems (1)
- feedback (1)
- fiction (1)
- financial markets (1)
- finite-state automata (1)
- floods (1)
- focus (1)
- focus particle (1)
- foregrounding (1)
- forgetting (1)
- forward / backward chaining (1)
- fried (1)
- function symbols (1)
- future curriculum (1)
- game-based learning (1)
- gaming (1)
- gamma-ray polarization (1)
- generalized logic programs (1)
- geomorphology (1)
- global change (1)
- group-subgroup relations (1)
- halide perovskites (1)
- hallow offshore (1)
- health crisis (1)
- high-energy astrophysical phenomena (1)
- historie intellecturelle (1)
- historie sociale (1)
- hospitals (1)
- human-AI interaction (1)
- hybrid simulation (1)
- hydrodynamic modeling (1)
- hydrodynamische Modellierung (1)
- identity management (1)
- immersion (1)
- improvement (1)
- impulsivity (1)
- industry 4.0 (1)
- infliximab (1)
- informatics (1)
- information flow control (1)
- information gateway (1)
- information status (1)
- integral Fourier operators (1)
- intention-behaviour gap (1)
- interventions (1)
- invasive aspects (1)
- is governance (1)
- it/business alignment (1)
- knowledge crystallization (1)
- knowledge management system (1)
- knowledge representation (1)
- knowledge transfers (1)
- language erp (1)
- learner characteristics (1)
- lebenslanges Lernen (1)
- legal history (1)
- levels of information systems research (process, enterprise-, ecosystem- & industry-level) (1)
- linical databases (1)
- literature review (1)
- long-time behaviour (1)
- lutein ester (1)
- macromolecular decay (1)
- makromolekularer Zerfall (1)
- manufacturing systems (1)
- mass loss (1)
- massereiche Sterne (1)
- massive stars (1)
- media literacy (1)
- mediated conversation (1)
- mental health (1)
- micro degree (1)
- micro- and nanotechnologies (1)
- micro-credential (1)
- microcredential (1)
- microlocal analysis (1)
- microlokale Analysis (1)
- middle aged / mental health (1)
- mindset (1)
- minorites (1)
- mobile technology (1)
- mobiles lernen (1)
- modelling (1)
- monoclonal antibodies (1)
- morphological analysis (1)
- mountainous rivers (1)
- multi-frequency (1)
- multi-valued logic (1)
- multicore architectures (1)
- narration (1)
- natural hazards (1)
- natural language processing (1)
- needs (1)
- neural networks (1)
- new product development (1)
- nonlinear dynamics (1)
- online courses (1)
- online photographs (1)
- online regrets (1)
- online teaching (1)
- open hardware (1)
- operating systems (1)
- operator calculus (1)
- organizational level (1)
- paraconsistency (1)
- parental mediation (1)
- participatory learning (1)
- pedagogical content knowledge (1)
- perception (1)
- personal development (1)
- persönliche Entwicklung (1)
- pitch accent (1)
- platform acceptance (1)
- primary school children (1)
- prior knowledge (1)
- privacy paradox (1)
- process modelling (1)
- product development (1)
- product generation engineering (1)
- production control (1)
- production engineering computing (1)
- production planning (1)
- production process (1)
- professional knowledge (1)
- program analysis (1)
- programming language (1)
- prominence (1)
- prosody (1)
- prototype (1)
- prototyping process (1)
- pseudodifferential operators (1)
- pseudodifferentiale Operatoren (1)
- radiative transfer (1)
- real-time measurement (1)
- reflection (1)
- regimen (1)
- regional studies (1)
- research challenges (1)
- research projects (1)
- retentivity (1)
- reusable aspects (1)
- reward system (1)
- rubicon model (1)
- rules (1)
- second-order conditioning (1)
- sectoral studies (1)
- security policies (1)
- self-organization (1)
- self-sovereign identity (1)
- semantics (1)
- semiconductors (1)
- sentiment analysis (1)
- service-oriented (1)
- sharing economy (1)
- singular manifolds (1)
- slavic literature (1)
- slavic studies (1)
- slavische Literatur (1)
- smartphone (1)
- social attraction (1)
- social networking sites (1)
- space mission (1)
- spatial economics (1)
- steam-dried (1)
- steamed (1)
- stellar winds (1)
- stratification (1)
- subject-oriented learning (1)
- sustainable product development (1)
- sustained negativity (1)
- symbols (1)
- symposium (1)
- systematic literature review (1)
- systems software (1)
- tacit knowledge (1)
- taxonomy (1)
- teacher education (1)
- teaching (1)
- teamwork (1)
- technologies (1)
- time-domain astronomy (1)
- top– down (1)
- trace data (1)
- transdiagnostic (1)
- trust (1)
- tuple spaces (1)
- twinning (1)
- universitäre Lehrerbildung (1)
- ventral striatum (1)
- verfassungsgerichtliche Kontrolle (1)
- views (1)
- violence (1)
- virtual learning environments (1)
- virtual machines (1)
- visual analytics (1)
- visual normalization theory (1)
- vocational training (1)
- web-tracking (1)
- weight perception (1)
- well-being (1)
- Älterer Mensch / Psychische Gesundheit (1)
- ökonomische Geographie (1)
Institut
- Extern (139)
- Fachgruppe Betriebswirtschaftslehre (59)
- Institut für Biochemie und Biologie (56)
- Department Sport- und Gesundheitswissenschaften (40)
- Institut für Ernährungswissenschaft (36)
- Department Psychologie (29)
- Institut für Künste und Medien (23)
- Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung (23)
- Institut für Informatik und Computational Science (20)
- Institut für Slavistik (17)
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.
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.
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.
Modeling expanding atmospheres is a difficult task because of the extreme non-LTE situation, the need to account for complex model atoms, especially for the iron-group elements with their millions of lines, and because of the supersonic expansion. Adequate codes have been developed e.g. by Hillier (CMFGEN), the Munich group (Puls, Pauldrach), and in Potsdam (PoWR code, Hamann et al.). While early work was based on the assumption of a smooth and homogeneous spherical stellar wind, the need to account for clumping became obvious about ten years ago. A relatively simple first-order clumping correction was readily implemented into the model codes. However, its simplifying assumptions are severe. Most importantly, the clumps are taken to be optically thin at all frequencies (”microclumping”). We discuss the consequences of this approximation and describe an approach to account for optically thick clumps (“macroclumping”). First results demonstrate that macroclumping can generally reduce the strength of spectral features, depending on their optical thickness. The recently reported discrepancy between the Hα diagnostic and the Pv resonance lines in O star spectra can be resolved without decreasing the mass-loss rates, when macroclumping is taken into account.
Clumping in Galactic WN stars : a comparison of mass loss rates from UV/optical & radio diagnostics
(2007)
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.
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.
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.
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.
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.
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.
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).
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.
While there is strong evidence for clumping in the winds of massive hot stars, very little is known about clumping in the winds from Central Stars. We have checked [WC]-type CSPN winds for clumping by inspecting the electron-scattering line wings. At least for three stars we found indications for wind inhomogeneities.
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.
Clumping in O-star winds
(2007)
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.
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.
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.
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?
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.
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.
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.
brandial06 was the tenth in a series of workshops that aims to bring together researchers working on the semantics and pragmatics of dialogues in fields such as artificial intelligence, formal semantics and pragmatics, computational linguistics, philosophy, and psychology. This volume collects all presented papers and posters and gives abstracts of the invited talks.
On the basis of the Dynamic Syntax framework, this paper argues that the production pressures in dialogue determining alignment effects and given versus new informational effects also drive the shift from case-rich free word order systems without clitic pronouns into systems with clitic pronouns with rigid relative ordering. The paper introduces assumptions of Dynamic Syntax, in particular the building up of interpretation through structural underspecification and update, sketches the attendant account of production with close coordination of parsing and production strategies, and shows how what was at the Latin stage a purely pragmatic, production-driven decision about linear ordering becomes encoded in the clitics in theMedieval Spanish system which then through successive steps of routinization yield the modern systems with immediately pre-verbal fixed clitic templates.
We analyze anaphoric phenomena in the context of building an input understanding component for a conversational system for tutoring mathematics. In this paper, we report the results of data analysis of two sets of corpora of dialogs on mathematical theorem proving. We exemplify anaphoric phenomena, identify factors relevant to anaphora resolution in our domain and extensions to the input interpretation component to support it.
Received views of utterance context in pragmatic theory characterize the occurrent subjective states of interlocutors using notions like common knowledge or mutual belief. We argue that these views are not compatible with the uncertainty and robustness of context-dependence in humanhuman dialogue. We present an alternative characterization of utterance context as objective and normative. This view reconciles the need for uncertainty with received intuitions about coordination and meaning in context, and can directly inform computational approaches to dialogue.
Goal-oriented dialog as a collaborative subordinated activity involving collective acceptance
(2006)
Modeling dialog as a collaborative activity consists notably in specifying the contain of the Conversational Common Ground and the kind of social mental state involved. In previous work (Saget, 2006), we claim that Collective Acceptance is the proper social attitude for modeling Conversational Common Ground in the particular case of goal-oriented dialog. We provide a formalization of Collective Acceptance, besides elements in order to integrate this attitude in a rational model of dialog are provided; and finally, a model of referential acts as being part of a collaborative activity is provided. The particular case of reference has been chosen in order to exemplify our claims.
A key problem for models of dialogue is to explain the mechanisms involved in generating and responding to clarification requests. We report a 'Maze task' experiment that investigates the effect of 'spoof' clarification requests on the development of semantic co-ordination. The results provide evidence of both local and global semantic co-ordination phenomena that are not captured by existing dialogue co-ordination models.
How does a shared lexicon arise in population of agents with differing lexicons, and how can this shared lexicon be maintained over multiple generations? In order to get some insight into these questions we present an ALife model in which the lexicon dynamics of populations that possess and lack metacommunicative interaction (MCI) capabilities are compared. We ran a series of experiments on multi-generational populations whose initial state involved agents possessing distinct lexicons. These experiments reveal some clear differences in the lexicon dynamics of populations that acquire words solely by introspection contrasted with populations that learn using MCI or using a mixed strategy of introspection and MCI. The lexicon diverges at a faster rate for an introspective population, eventually collapsing to one single form which is associated with all meanings. This contrasts sharply with MCI capable populations in which a lexicon is maintained, where every meaning is associated with a unique word. We also investigated the effect of increasing the meaning space and showed that it speeds up the lexicon divergence for all populations irrespective of their acquisition method.
Demonstratives, in particular gestures that "only" accompany speech, are not a big issue in current theories of grammar. If we deal with gestures, fixing their function is one big problem, the other one is how to integrate the representations originating from different channels and, ultimately, how to determine their composite meanings. The growing interest in multi-modal settings, computer simulations, human-machine interfaces and VRapplications increases the need for theories ofmultimodal structures and events. In our workshopcontribution we focus on the integration of multimodal contents and investigate different approaches dealing with this problem such as Johnston et al. (1997) and Johnston (1998), Johnston and Bangalore (2000), Chierchia (1995), Asher (2005), and Rieser (2005).
A new method is used in an eye-tracking pilot experiment which shows that it is possible to detect differences in common ground associated with the use of minimally different types of indefinite anaphora. Following Richardson and Dale (2005), cross recurrence quantification analysis (CRQA) was used to show that the tandem eye movements of two Swedish-speaking interlocutors are slightly more coupled when they are using fully anaphoric indefinite expressions than when they are using less anaphoric indefinites. This shows the potential of CRQA to detect even subtle processing differences in ongoing discourse.
Verbal or visual? : How information is distributed across speech and gesture in spatial dialog
(2006)
In spatial dialog like in direction giving humans make frequent use of speechaccompanying gestures. Some gestures convey largely the same information as speech while others complement speech. This paper reports a study on how speakers distribute meaning across speech and gesture, and depending on what factors. Utterance meaning and the wider dialog context were tested by statistically analyzing a corpus of direction-giving dialogs. Problems of speech production (as indicated by discourse markers and disfluencies), the communicative goals, and the information status were found to be influential, while feedback signals by the addressee do not have any influence.
We describe an experiment to gather original data on geometrical aspects of pointing. In particular, we are focusing upon the concept of the pointing cone, a geometrical model of a pointing’s extension. In our setting we employed methodological and technical procedures of a new type to integrate data from annotations as well as from tracker recordings. We combined exact information on position and orientation with rater’s classifications. Our first results seem to challenge classical linguistic and philosophical theories of demonstration in that they advise to separate pointings from reference.
Classical SDRT (Asher and Lascarides, 2003) discussed essential features of dialogue like adjacency pairs or corrections and up-dating. Recent work in SDRT (Asher, 2002, 2005) aims at the description of natural dialogue. We use this work to model situated communication, i.e. dialogue, in which sub-sentential utterances and gestures (pointing and grasping) are used as conventional modes of communication. We show that in addition to cognitive modelling in SDRT, capturing mental states and speech-act related goals, special postulates are needed to extract meaning out of contexts. Gestural meaning anchors Discourse Referents in contextually given domains. Both sorts of meaning are fused with the meaning of fragments to get at fully developed dialogue moves. This task accomplished, the standard SDRT machinery, tagged SDRSs, rhetorical relations, the up-date mechanism, and the Maximize Discourse Coherence constraint generate coherent structures. In sum, meanings from different verbal and non-verbal sources are assembled using extended SDRT to form coherent wholes.
We present a formal analysis of iconic coverbal gesture. Our model describes the incomplete meaning of gesture that’s derivable from its form, and the pragmatic reasoning that yields a more specific interpretation. Our formalism builds on established models of discourse interpretation to capture key insights from the descriptive literature on gesture: synchronous speech and gesture express a single thought, but while the form of iconic gesture is an important clue to its interpretation, the content of gesture can be resolved only by linking it to its context.
In two experiments, many annotators marked antecedents for discourse deixis as unconstrained regions of text. The experiments show that annotators do converge on the identity of these text regions, though much of what they do can be captured by a simple model. Demonstrative pronouns are more likely than definite descriptions to be marked with discourse antecedents. We suggest that our methodology is suitable for the systematic study of discourse deixis.
We present a new analysis of illocutionary forces in dialogue. We analyze them as complex conversational moves involving two dimensions: what Speaker commits herself to and what she calls on Addressee to perform. We start from the analysis of speech acts such as confirmation requests or whimperatives, and extend the analysis to seemingly simple speech acts, such as statements and queries. Then, we show how to integrate our proposal in the framework of the Grammar for Conversation (Ginzburg, to app.), which is adequate for modelling agents' information states and how they get updated.
Claiming that cross-speaker "but" can signal correction in dialogue, we start by describing the types of corrections "but" can communicate by focusing on the Speech Act (SA) communicated in the previous turn and address the ways in which "but" can correct what is communicated. We address whether "but" corrects the proposition, the direct SA or the discourse relation communicated in the previous turn. We will also briefly address other relations signalled by cross-turn "but". After presenting a typology of the situations "but" can correct, we will address how these corrections can be modelled in the Information State model of dialogue, motivating this work by showing how it can be used to potentially avoid misunderstandings. We wrap up by showing how the model presented here updates beliefs in the Information State representation of the dialogue and can be used to facilitate response deliberation.
An account is presented of the focus properties, common ground effect and dialogue behaviour of the accented German discourse marker "doch" and the accented sentence negation "nicht". It is argued that "doch" and "nicht" evoke as a focus alternative the logical complement of the proposition expressed by the sentence in which they occur, and that an analysis in terms of contrastive focus accounts for their effect on the common ground and their function in dialogue.
We present an analysis of student language input in a corpus of tutoring dialogue in the domain of symbolic differentiation. Our focus on procedural tutoring makes the dialogue comparable to collaborative problem-solving (CPS). Existing CPS models describe the process of negotiating plans and goals, which also fits procedural tutoring. However, we provide a classification of student utterances and corpus annotation which shows that approximately 28% of non-trivial student language in this corpus is not accounted for by existing models, and addresses other functions, such as evaluating past actions or correcting mistakes. Our analysis can be used as a foundation for improving models of tutoring dialogue.
We present an extension to a comprehensive context model that has been successfully employed in a number of practical conversational dialogue systems. The model supports the task of multimodal fusion as well as that of reference resolution in a uniform manner. Our extension consists of integrating implicitly mentioned concepts into the context model and we show how they serve as candidates for reference resolution.