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Статті в журналах з теми "Stellar feedbacks"
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Ciardi, B. "Inhomogeneous reionization regulated by radiative and stellar feedbacks." Astronomical & Astrophysical Transactions 20, no. 1 (2001): 177–82. http://dx.doi.org/10.1080/10556790108208210.
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Ekström, Sylvia, Georges Meynet, Cyril Georgy, José Groh, Arthur Choplin, and Hanfeng Song. "Massive star evolution: feedbacks in low-Z environment." Proceedings of the International Astronomical Union 14, S344 (2018): 153–60. http://dx.doi.org/10.1017/s1743921318007238.
Повний текст джерелаАнотація:
AbstractMassive stars are the drivers of the chemical evolution of dwarf galaxies. We review here the basics of massive star evolution and the specificities of stellar evolution in low-Z environment. We discuss nucleosynthetic aspects and what observations could constrain our view on the first generations of stars.
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Ciardi, B., A. Ferrara, F. Governato, and A. Jenkins. "Inhomogeneous reionization of the intergalactic medium regulated by radiative and stellar feedbacks." Monthly Notices of the Royal Astronomical Society 314, no. 3 (2000): 611–29. http://dx.doi.org/10.1046/j.1365-8711.2000.03365.x.
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Dekel, Avishai, Nir Mandelker, Frederic Bournaud, Daniel Ceverino, Yicheng Guo, and Joel Primack. "Clump survival and migration in VDI galaxies: an analytical model versus simulations and observations." Monthly Notices of the Royal Astronomical Society 511, no. 1 (2022): 316–40. http://dx.doi.org/10.1093/mnras/stab3810.
Повний текст джерелаАнотація:
ABSTRACT We address the nature of the giant clumps in high-z galaxies that undergo violent disc instability, distinguishing between long-lived and short-lived clumps. We study the evolution of long-lived clumps during migration through the disc via an analytical model tested by simulations and confront theory with CANDELS-HST observations. The clump ‘bathtub’ model, which considers gas and stellar gain and loss, involves four parameters: the accretion efficiency α, the star formation rate (SFR) efficiency ϵd, and the outflow mass-loading factors for gas and stars, η and ηs. The corresponding time-scales are comparable to the migration time, two-three orbital times. The accretion-rate dependence on clump mass, gas, and stars, allows an analytical solution involving exponential growing and decaying modes. For the fiducial parameter values there is a main evolution phase where the SFR and gas mass are constant and the stellar mass is rising linearly with time. This makes the inverse specific SFR an observable proxy for clump age. When η or ϵd are high, or α is low, the decaying mode induces a decline of SFR and gas mass till the migration ends. Later, the masses and SFR approach an hypothetical exponential growth with a constant specific SFR. The model matches simulations with different, moderate feedbacks, both in isolated and cosmological settings. The observed clumps agree with our predictions, indicating that the massive clumps are long-lived and migrating. A challenge is to model feedback that is non-disruptive in massive clumps but suppresses SFR to match the galactic stellar-to-halo mass ratio.
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Locci, Daniele, Antonino Petralia, Giuseppina Micela, Antonio Maggio, Angela Ciaravella, and Cesare Cecchi-Pestellini. "Extreme-ultraviolet- and X-Ray-driven Photochemistry of Gaseous Exoplanets." Planetary Science Journal 3, no. 1 (2022): 1. http://dx.doi.org/10.3847/psj/ac3f3c.
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Abstract The interaction of exoplanets with their host stars causes a vast diversity in bulk and atmospheric compositions and physical and chemical conditions. Stellar radiation, especially at the shorter wavelengths, drives the chemistry in the upper atmospheric layers of close orbiting gaseous giants, providing drastic departures from equilibrium. In this study, we aim at unfolding the effects caused by photons in different spectral bands on the atmospheric chemistry. This task is particularly difficult because the characteristics of chemical evolution emerge from many feedbacks on a wide range of timescales, and because of the existing correlations among different portions of the stellar spectrum. In describing the chemistry, we have placed particular emphasis on the molecular synthesis induced by X-rays. The weak X-ray photoabsorption cross sections of the atmospheric constituents boost the gas ionization to pressures inaccessible to vacuum and extreme-ultraviolet photons. Although X-rays interact preferentially with metals, they produce a secondary electron cascade able to ionize efficiently hydrogen- and helium-bearing species, giving rise to a distinctive chemistry.
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Fierlinger, Katharina M., Andreas Burkert, Evangelia Ntormousi, et al. "Stellar feedback efficiencies: supernovae versus stellar winds." Monthly Notices of the Royal Astronomical Society 456, no. 1 (2015): 710–30. http://dx.doi.org/10.1093/mnras/stv2699.
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Forget, F., and J. Leconte. "Possible climates on terrestrial exoplanets." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2014 (2014): 20130084. http://dx.doi.org/10.1098/rsta.2013.0084.
Повний текст джерелаАнотація:
What kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance, to optimize future telescopic observations or to assess the probability of habitable worlds. To begin with, climate primarily depends on (i) the atmospheric composition and the volatile inventory; (ii) the incident stellar flux; and (iii) the tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side. The atmospheric composition and mass depends on complex processes, which are difficult to model: origins of volatiles, atmospheric escape, geochemistry, photochemistry, etc. We discuss physical constraints, which can help us to speculate on the possible type of atmosphere, depending on the planet size, its final distance for its star and the star type. Assuming that the atmosphere is known, the possible climates can be explored using global climate models analogous to the ones developed to simulate the Earth as well as the other telluric atmospheres in the solar system. Our experience with Mars, Titan and Venus suggests that realistic climate simulators can be developed by combining components, such as a ‘dynamical core’, a radiative transfer solver, a parametrization of subgrid-scale turbulence and convection, a thermal ground model and a volatile phase change code. On this basis, we can aspire to build reliable climate predictors for exoplanets. However, whatever the accuracy of the models, predicting the actual climate regime on a specific planet will remain challenging because climate systems are affected by strong positive feedbacks. They can drive planets with very similar forcing and volatile inventory to completely different states. For instance, the coupling among temperature, volatile phase changes and radiative properties results in instabilities, such as runaway glaciations and runaway greenhouse effect.
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Herbst, Konstantin, John Lee Grenfell, Miriam Sinnhuber, et al. "A new model suite to determine the influence of cosmic rays on (exo)planetary atmospheric biosignatures." Astronomy & Astrophysics 631 (October 31, 2019): A101. http://dx.doi.org/10.1051/0004-6361/201935888.
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Context. The first opportunity to detect indications for life outside of the Solar System may be provided already within the next decade with upcoming missions such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (E-ELT) and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) mission, searching for atmospheric biosignatures on planets in the habitable zone of cool K- and M-stars. Nevertheless, their harsh stellar radiation and particle environment could lead to photochemical loss of atmospheric biosignatures. Aims. We aim to study the influence of cosmic rays on exoplanetary atmospheric biosignatures and the radiation environment considering feedbacks between energetic particle precipitation, climate, atmospheric ionization, neutral and ion chemistry, and secondary particle generation. Methods. We describe newly combined state-of-the-art modeling tools to study the impact of the radiation and particle environment, in particular of cosmic rays, on atmospheric particle interaction, atmospheric chemistry, and the climate-chemistry coupling in a self-consistent model suite. To this end, models like the Atmospheric Radiation Interaction Simulator (AtRIS), the Exoplanetary Terrestrial Ion Chemistry model (ExoTIC), and the updated coupled climate-chemistry model are combined. Results. In addition to comparing our results to Earth-bound measurements, we investigate the ozone production and -loss cycles as well as the atmospheric radiation dose profiles during quiescent solar periods and during the strong solar energetic particle event of February 23, 1956. Further, the scenario-dependent terrestrial transit spectra, as seen by the NIR-Spec infrared spectrometer onboard the JWST, are modeled. Amongst others, we find that the comparatively weak solar event drastically increases the spectral signal of HNO3, while significantly suppressing the spectral feature of ozone. Because of the slow recovery after such events, the latter indicates that ozone might not be a good biomarker for planets orbiting stars with high flaring rates.
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D'Antona, Francesca. "Stellar evolution and feedback connections to stellar dynamics." Proceedings of the International Astronomical Union 2, no. 14 (2006): 430–31. http://dx.doi.org/10.1017/s1743921307011222.
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AbstractUntil a few years ago, the common paradigm for the formation of Globular Clusters (GCs) was that they constitute a ‘simple stellar population’ in which all the stars were formed from a chemically homogeneous cluster medium within a relatively short interval of time, at the beginning of the galactic life. In recent years, the spectroscopic information on the low luminosity (turnoff) cluster stars have extended to the unevolved stars the recognition that chemical anomalies are a common feature of GCs and not an exception. This has provoked a revolution in the simple view of GC formation, and requires an adequate dynamical modelling including gas dynamics. It is by now well accepted that at least two different stellar components are common in most GCs. These are almost unequivocally identified with (i) a first stellar generation, which gave origin to stars of all masses; and (ii)) a second generation, born from the ejecta of the most massive asymptotic giant branch stars of the first generation, in the first 100–200 Myr from the first burst of star formation. A ‘third’ population is present only in some GCs, and is more difficult to be understood. It is characterized by stars having a huge helium content (Y ≃ 0.4, if stellar modelling is reasonable) and extreme chemical anomalies in the proton capture elements (Na, O, Al). The status of understanding of the GC properties, based on our most recent models of stellar evolution, is discussed.
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Ivanova, Nataliya M. "Stellar dynamics and feedback connections to stellar evolution." Proceedings of the International Astronomical Union 2, no. 14 (2006): 432–33. http://dx.doi.org/10.1017/s1743921307011234.
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AbstractIn dense stellar systems, dynamical interactions between objects inevitably lead to frequent formation of exotic stellar objects and multiple systems, thereby imposing new questions for the stellar evolution theory. The evolutionary path of such systems could be different from that of the unperturbed objects, therefore, we must re-evaluate their evolutionary treatment to clarify their consequent dynamical evolution. We review briefly the classes of important dynamical encounters and discuss several post-encounter outcomes that may require more detailed attention or development of a new treatment in stellar evolution: evolution of complex merger products, spun-up stars, binaries with stripped giants and triples.
Дисертації з теми "Stellar feedbacks"
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Maillard, Vincent. "Modèle des fronts de photoevaporation dans les régions de formation d'étoiles." Electronic Thesis or Diss., Université Paris sciences et lettres, 2023. http://www.theses.fr/2023UPSLO003.
Повний текст джерелаАнотація:
Les conditions de formation des étoiles est un sujet central en astrophysique. Le taux de formation stellaire (SFR) est relié à la masse de gaz moléculaire par la relation de Schmidt-Kennicutt. Une étoile modifie son nuage parent grâce aux vents, jets et à son rayonnement, balayant son environnement, détruisant des sites de formation d’étoiles, mais pouvant aussi en compresser et déstabiliser, déclenchant la formation de nouvelles étoiles. Ma thèse s’est concentrée sur la rétroaction radiative, largement dominée par celle des étoiles massives. Cela crée une région ionisée en expansion au plus près de l’étoile, suivie d’une région où l’hydrogène moléculaire est dissocié (photodissociation region en anglais, ou PDR), trop chaude pour former des étoiles. De nombreux modèles physico-chimiques des PDRs cherchent un état stationnaire, négligeant la dynamique du gaz. Des observations Herschel en CO excité et ALMA (Atacama Large Millimeter Array) en CH+ et SH+ ont changé la vision stationnaire de la structure des PDRs en soulignant le rôle de la dynamique du gaz. Le bord des nuages se trouve être à haute pression, fortement corrélée à l’intensité du champ UV incident. Le mécanisme de photo-évaporation peut reproduire ces caractéristiques: avec l’évaporation à haute vitesse du gaz chaud ionisé, l’effet fusée fait se propager une onde de pression dans le nuage, expliquant les hautes pressions observées. Par l’érosion du nuage, la frontière avec le milieu ionisé, le front d’ionisation (IF), avance dans le milieu neutre. Les modèles PDRs tant numériques que théoriques doivent être mis à jour pour prendre en compte cette propagation de l’IF. Nous avons d’abord construit un modèle semi-analytique de la transition entre le gaz atomique et moléculaire (H/H2) tenant compte de l’avancement de l’IF. Nous avons montré que la largeur de la région atomique est réduite comparé à des modèles statiques. Elle peut même disparaître si la vitesse de l’IF dépasse une valeur seuil, menant à la fusion de l’IF et de la transition H/H2. Nous avons trouvé des formules pour estimer ce seuil ainsi que la colonne densité totale de H atomique. En comparant notre théorie avec des observations de PDRs, nous avons montré que les effets de la dynamique sont forts, en particulier pour les PDRs faiblement illuminées comme la nébuleuse de la Tête de Cheval. En préparation des observations JWST de H2, nous avons implémenté le calcul des populations des niveaux de H2 dans le code Hydra, un code hydro-dynamique dépendant du temps modélisant les PDRs en photo-évaporation. L’étude précédente nous a permis de conclure que les effets dynamiques amène du H2 dans une région plus chaude et plus illuminée. Le rapprochement de la transition H/H2 réduit l'intensité absorbée par les poussière, qui est alors convertie en pompage UV de H2 (amplification d'un facteur 6 trouvé pour la Barre d'Orion mais peu efficace dans la Tête de Cheval). En addition, nous avons étudié des observations ALMA de la Tête de Cheval à haute résolution spatiale montrant une grande proximité entre l’IF et la molécule CO, présente habituellement profondément dans le nuage. Nous trouvons une borne supérieure à la largeur de la région atomique à quelques centaines d’unités astronomiques. Nous trouvons que le code PDR statique et stationnaire de Meudon reproduit la largeur de la région atomique sous la contrainte, tout comme les modèles dynamiques. Ces observations ne permettent donc pas de contraindre les effets dynamiques.Nous avons effectué une étude d’observations à haute résolution spectrale de raies d’émission de H2 faites par le spectrographe IGRINS. Nous montrons que les rapports de raies contraignent peu les conditions physiques, mais que le peuplement des états de H2 est fortement influé par des relaxations induites par collision, contrairement à l'image classique d'une cascade majoritairement radiative après pompage UV<br>The conditions of formation of stars is a fundamental question of astrophysics. The star formation rate (SFR) is linked to the mass of molecular gas by the Schmidt-Kennicutt relation. However, a star applies some feedbacks on its parent cloud in the form of winds, jets and radiation. They sweep their environment, destroying other star formation sites, but can also compress and destabilize them, triggering the formation of new stars. My thesis focused on the radiative feedback, which is vastly dominated by the one of massive stars. It creates an expanding region where the gas is ionized close to the star, followed by a region where the chemistry is dominated by photons capable of dissociating molecular hydrogen (photodissociation region, or PDR) which includes a layer of atomic hydrogen, which is too hot to form stars. Its width informs us about the fraction of gaz unable to form stars. Numerous models describe the physics and chemistry of PDRs by looking for a stationary state, and neglecting the gas dynamics. However, new observations made by Hershel in excited CO, and by the Atacama Large Millimeter Array (ALMA) in CH+ and SH+ have changed the stationary vision of PDR structure by highlighting the role of the gas dynamics. The edge of clouds is found to be a high-pressure environment, which is strongly correlated to the impinging UV field intensity. The photo-evaporation mechanism is capable of reproducing those features: with the high-speed evaporation of hot ionized gas, the rocket effect makes a pressure wave propagate inside the cloud, explaining the high pressures observed. By the erosion of the cloud, the border withe the ionized medium, the ionization front (IF) advances into the neutral medium. PDR models have to be updated to take into account the propagation of the IF.We built a semi-analytical model of the transition between atomic and molecular gas (H/H2) including the advancing IF. We obtained that the width of the atomic region is reduced compared to static models. It can also disappear if the IF velocity exceeds a threshold value, leading to the merging of the IF and the H/H2 transition. We found analytical formulas to estimate this threshold as well as the total column density of atomic H. By comparing our theory to PDRs observations, we showed that the dynamical effects are strong, especially in the case of weakly illuminated PDRs such as the Horsehead.To prepare for the JWST observations of H2, we have implemented the computation of H2 levels in the Hydra code, which is a hydro-dynamic, time dependent code that models the physics and chemistry of photo-evaporating PDRs. The precedent study allowed to conclude that dynamical effects bring some H2 in a hotter and more illuminated region. The reduction of the IF-H/H2 distance reduces the intensity absorbed by dust, which is then converted to UV-pumping of H2 (amplification by a factor 6 for the Orion Bar, but not efficient in the Horsehead).In addition, we studied ALMA observations of the Horsehead with high spatial resolution. They show a great proximity between the IF and the CO line emission, usually present deep in the cloud. We find an upper limit of a few hundred astronomical units for the width of the atomic region. We find that isobaric, static and stationary Meudon PDR models reproduce the width of the atomic region within the limit found, and so does the dynamical models. These observations therefore do not allow us ton constrain dynamical effects.We performed a study on high spectral resolution observations of rotation-vibration lines of H2 made by the IGRINS spectrograph. We show that the line ratios do not constrain well the physical conditions, but that the population of the states of H2 are much influenced by relaxation rates induced by collisions, unlike the classical picture of a cascade mainly dominated by radiation after the UV pumping
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Rogers, Hazel Claire. "Feedback from winds and supernovae in massive stellar clusters." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/6858/.
Повний текст джерелаАнотація:
This thesis contains a study of the mechanical feedback from winds and supernovae on inhomogeneous molecular material left over from the formation of a massive stellar cluster. Firstly, the mechanical input from a cluster with three massive O-stars into a giant molecular cloud (GMC) clump containing 3240M⊙ of molecular material within a 4 pc radius is investigated using a 3D hydrodynamcial model. The cluster wind blows out of the molecular clump along low-density channels, into which denser clump material is entrained. The densest regions are surprisingly resistant to ablation by the cluster wind, in part due to shielding by other dense regions close to the cluster. Nonetheless, molecular material is gradually removed by the cluster wind during which mass-loading factors in excess of several hundred are obtained. Because the clump is very porous, 60-75% of the injected wind energy escapes the simulation domain. After 4.4Myrs the massive stars in the simulation start to explode as supernovae. The highly structured environment into which the SN energy is released allows even weaker coupling to the remaining dense material and practically all of the SN energy reaches the wider environment. Secondly, the X-ray emission from the simulated stellar cluster is presented. The GMC clump causes short–lived attenuation effects on the X-ray emission of the cluster. However, once most of the material has been ablated away by the winds the remaining dense clumps do not have a noticable effect on the attenuation compared with the assumed interstellar medium (ISM) column. The evolution of the X-ray luminosity and spectra are presented, and synthetic images of the emission are generated. The X-ray luminosity is initially high whilst the winds are “bottled up”, but reduce to a near constant value once the GMC clump has been mostly destroyed. The luminosity decreases slighly during the red supergiant phase of the stars due to the depressurization of the hot gas. However, the luminosity dramatically increases during the Wolf-Rayet stage of each star. The X-ray luminosity is enhanced by 2-3 orders of magnitude for at least 466 yrs after each supernova explosion, at which time the blast wave leaves the grid. Comparisons between the simulated cluster and both theoretical models and observations of young stellar clusters are presented. Thirdly, the radio emission from the simulated cluster is presented. Similar to the X-ray emission, the thermal radio emission is intially high when the winds are confined in the GMC clump and reduce as the material is ablated away. The evolution of the radio flux density and spectra are presented, and synthetic images of the emission are generated. The radio emission is compared with the X-ray results throughout the evolution of the cluster. The flux density increases during the RSG phase, and remains high during the WR phgase of the stars. The radio flux density is enhanced by three orders of magnitude during the first supernova explosion. Comparisons between the simulated cluster and observations of young stellar clusters are made. Finally, a preliminary investigation of the interaction of stellar winds within a massive cluster are presented. The hydrodynamcial simulations examine the energy and mass input of a stellar cluster into the ISM.
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Giarrusso, Daniele. "Properties of the galactic-scale gas circulation generated by stellar feedback." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20942/.
Повний текст джерелаАнотація:
Questo lavoro di tesi si propone di esaminare la simulazione di una galassia isolata simile alla Via Lattea e, in particolare, di analizzare i processi di feedback dovuto ad esplosioni di supernove, il meccanismo responsabile della generazione di outflow gassosi dal disco. Scopo della tesi è quello di testare la validità dei risultati ottenuti dalla simulazione (generata dal recente modello di feedback SMUGGLE presente nel codice a griglia mobile AREPO) dal punto di vista della formazione stellare, del tasso di esplosioni di supernove e dei fenomeni di outflow di gas su scala galattica. Sono stati indagati vari andamenti evolutivi delle proprietà cinematiche del gas, della formazione stellare e dell'efficienza di rilascio di energia/impulso da parte delle supernove al fine di ricercare relazioni che mettano in luce lo stretto legame tra questi processi astrofisici. La simulazione è stata in grado di generare fenomeni di esplusione di gas in maniera auto-consistente e, in combinazione con l'esaurirsi del gas a causa della formazione stellare, ha condotto la galassia a regolare il suo tasso di formazione stellare e quello relativo alle esplosioni di supernove a dei livelli in accordo con le osservazioni. Inoltre la simulazione è stata in grado di riprodurre la relazione osservativa di Kennicutt-Schmidt. Infine questo lavoro di tesi ha evidenziato una possibile connessione tra la variazione del tasso di densita' superficiale di formazione stellare (SFRD) e l'ammontare di massa di gas esplusa dal disco. Ciò è stato fatto al fine di valutare l'esistenza di un possibile valore critico per la SFRD tale per cui, al di sopra di questa soglia, si possano chiaramente osservare fenomeni di espulsione di gas su scala galattica. I risultati ottenuti però non mostrano evidenze dell'esistenza di un tale valore e che ulteriori approfondimenti e simulazioni di confronto sono necessari per avvalorare questi risultati preliminari.
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Rey, Raposo Ramon. "The interplay between stellar feedback and galactic environment in molecular clouds." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/21022.
Повний текст джерелаАнотація:
In this thesis we address the problem of understanding the star formation process in giant molecular clouds in a galactic context. Most simulations of molecular clouds to date use an oversimplified set of initial conditions (turbulent spheres/boxes or colliding flows). Full galactic scale models are able to generate molecular clouds with complex morphologies and velocity fields but they fail to reproduce in detail the effects that occur at sub-pc scales (e.g. stellar feedback). Our goal is to build the bridge between these two scenarios, and to model the star formation process in molecular clouds produced in a galactic context. We extract our molecular clouds from full-scale galactic simulations, hence we need to increase the resolution by two orders of magnitude. We introduce the details of the program used to simulate molecular clouds in Chapter 2, and describe in detail the method we follow to increase the resolution of the galactic clouds. In Chapter 3 we compare our simulated galactic clouds with the more conventional approach of using turbulent spheres. We create turbulent spheres to match the virial state of three galactic clouds. We perform isothermal simulations and find that the velocity field inherited from the full-scale galactic simulations plays an important role in the star formation process. Clouds affected by strong galactic shear produce less stars compared with clouds that are compressed. We define (and test) a set of parameters to characterise the dynamical state of our clouds. To include stellar feedback in our simulations we need to introduce a cooling/heating algorithm. In Chapter 4 we analyse how the different velocity fields of our clouds change the temperature distribution even in the absence of feedback. To study the formation of molecules we need to model the chemistry of H2 in our clouds. We also add CO chemistry, and produce synthetic observations of our clouds. The effect of feedback from winds and supernovae in galactic clouds is studied in Chapter 5. We analyse the effect of winds in clouds with very different velocity fields. We find that the effect of winds is stronger in highly virialised, high star forming clouds, with clouds with weak galactic shear, compared to unbound shear-dominated clouds. The steady and continuous action of the winds appears to have a greater effect than the supernovae. In summary, the inherited properties from the galaxy have an impact on many relevant processes in star formation, influencing gravitational collapse, the formation of filamentary structures, the temperature field of the cloud, and have a considerable effect on the impact of feedback in the clouds.
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Smith, Matthew Carey. "Modelling star formation and stellar feedback in numerical simulations of galaxy formation." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277830.
Повний текст джерелаАнотація:
Remarkable progress has been made over the last few decades in furthering our understanding of the growth of cosmic structure. Nonetheless, there remains a great deal of uncertainty regarding the precise details of the complex baryonic physics that regulate galaxy formation. Any theory of star formation in galaxies must encompass the radiative cooling of gas into dark matter haloes, the formation of a turbulent, multiphase interstellar medium (ISM), the efficiency with which molecular gas is able to collapse into cores and ultimately stars, and the subsequent interaction of those stars with the gas through ionizing radiation, winds and supernova (SN) explosions. Given the highly non-linear nature of the problem, numerical simulations provide an invaluable tool with which to study galaxy formation. Yet, even with contemporary computational resources, the inherently large dynamical range of spatial scales that must be tackled makes the development of such models extremely challenging, inevitably leading to the adoption of `subgrid' approximations at some scale. In this thesis, I explore new methods of incorporating the physics of star formation and stellar feedback into high resolution hydrodynamic simulations of galaxies. I first describe a new implementation of star formation and SN feedback that I have developed for the state-of-the-art moving mesh code Arepo. I carry out a detailed study into various classes of subgrid SN feedback schemes commonly adopted in the literature, including injections of thermal and/or kinetic energy, two parametrizations of delayed cooling feedback and a 'mechanical' feedback scheme that injects the appropriate amount of momentum depending on the relevant scale of the SN remnant (SNR) resolved. All schemes make use of individually time-resolved SN events. Adopting isolated disk galaxy setups at different resolutions, with the highest resolution runs reasonably resolving the Sedov-Taylor phase of the SNR, I demonstrate that the mechanical scheme is the only physically well-posed method of those examined, is efficient at suppressing star formation, agrees well with the Kennicutt-Schmidt relation and leads to converged star formation rates and galaxy morphologies with increasing resolution without fine tuning any parameters. However, I find that it is difficult to produce outflows with high enough mass loading factors at all but the highest resolution. I discuss the various possible solutions to this effect, including improved modelling of star formation. Moving on to a more self-consistent setup, I carry out a suite of cosmological zoom-in simulations of low mass haloes at very high resolution, performed to z = 4, to investigate the ability of SN feedback models to produce realistic galaxies. The haloes are selected in a variety of environments, ranging from voids to crowded locations. In the majority of cases, SN feedback alone has little impact at early times even in low mass haloes ($\sim10^{10}\,\mathrm{M_\odot}$ at z = 0). This appears to be due largely to the build up of very dense gas prior to SN events, suggesting that other mechanisms (such as other stellar feedback processes) are required to regulate ISM properties before SNe occur. The effectiveness of the feedback also appears to be strongly dependent on the merger history of the halo. Finally, I describe a new scheme to drive turbulence in isolated galaxy setups. The turbulent structure of the ISM very likely regulates star formation efficiencies on small scales, as well as affecting the clustering of SNe. The large range of potential drivers of ISM turbulence are not fully understood and are, in any case, unlikely to arise ab initio in a whole galaxy simulation. I therefore neglect these details and adopt a highly idealised approach, artificially driving turbulence to produce an ISM structure of my choice. This enables me to study the effects of a given level of ISM turbulence on global galaxy properties, such as the fragmentation scale of the disk and the impact on SN feedback efficiencies. I demonstrate this technique in the context of simulations of isolated dwarfs, finding that moderate levels of turbulent driving in combination with SN feedback can produce a steady-state of star formation rates and global galaxy properties, rather than the extremely violent SN feedback that is produced by a rapidly fragmenting disk.
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Jose, Jessy, Jinyoung S. Kim, Gregory J. Herczeg, et al. "STAR FORMATION IN W3—AFGL 333: YOUNG STELLAR CONTENT, PROPERTIES, AND ROLES OF EXTERNAL FEEDBACK." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621216.
Повний текст джерелаАнотація:
One of the key questions in the field of star formation is the role of stellar feedback on the subsequent star formation process. The W3 giant molecular cloud complex at the western border of the W4 super bubble is thought to be influenced by the massive stars in W4. This paper presents a study of the star formation activity within AFGL. 333, a similar to 104 M-circle dot cloud within W3, using deep JHK(s) photometry obtained from the NOAO Extremely Wide Field Infrared Imager combined with Spitzer IRAC and MIPS photometry. Based on the infrared excess, we identify 812 candidate young stellar objects (YSOs) in the complex, of which 99 are Class I and 713 are Class II sources. The stellar density analysis of YSOs reveals three major stellar aggregates within AFGL. 333, namely AFGL. 333 Main, AFGL. 333 NW1 and AFGL. 333 NW2. The disk fraction within AFGL. 333 is estimated to be similar to 50%-60%. We use the extinction map made from the H - K-s colors of the background stars and CO data to understand the cloud structure and to estimate the cloud mass. From the stellar and cloud mass associated with AFGL. 333, we infer that the region is currently forming stars with an efficiency of similar to 4.5% and at a rate of similar to 2-3M(circle dot) Myr(-1) pc(-2). In general, the star formation activity within AFGL. 333 is comparable to that of nearby low mass star-forming regions. We do not find any strong evidence to suggest that the stellar feedback from the massive stars of nearby W4 super bubble has affected the global star formation properties of the AFGL. 333 region.
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Lochhaas, Cassandra Derrick. "Stellar Feedback in Galaxies, Its Impact on the Circumgalactic Medium, and the Importance of Radiative Cooling." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1562676332648711.
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Grisdale, Kearn. "The role of stellar feedback on the structure of the ISM and star formation in galaxies." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/841384/.
Повний текст джерелаАнотація:
Stellar feedback refers to the injection of energy, momentum and mass into the interstellar medium (ISM) by massive stars. This feedback owes to a combination of ionising radiation, radiation pressure, stellar winds and supernovae and is likely responsible both for the inefficiency of star formation in galaxies, and the observed super-sonic turbulence of the ISM. In this thesis, I study how stellar feedback shapes the ISM thereby regulating galaxy evolution. In particular, I focus on three key questions: (i) How does stellar feedback shape the gas density distribution of the ISM? (ii) How does feedback change or influence the distribution of the kinetic energy in the ISM? and (iii) What role does feedback play in determining the star formation efficiency of giant molecular clouds (GMCs)? To answer these questions, I run high resolution (dx~4.6 pc) numerical simulations of three isolated galaxies, both with and without stellar feedback. I compare these simulations to observations of six galaxies from The HI Nearby Galaxy Survey (THINGS) using power spectra, and I use clump finding techniques to identify GMCs in my simulations and calculate their properties. I find that the kinetic energy power spectra in stellar feedback- regulated galaxies, regardless of the galaxy's mass and size, show scalings in excellent agreement with supersonic turbulence on scales below the thickness of the HI layer. I show that feedback influences the gas density field, and drives gas turbulence, up to large (kiloparsec) scales. This is in stark contrast to the density fields generated by large-scale gravity-only driven turbulence (i.e. without stellar feedback). Simulations with stellar feedback are able to reproduce the internal properties of GMCs such as: mass, size and velocity dispersion. Finally, I demonstrate that my simulations naturally reproduce the observed scatter (3.5-4 dex) in the star formation efficiency per free-fall time of GMCs, despite only employing a simple Schmidt star formation law. I conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales and that stellar feedback is, therefore, key to regulating the evolution of galaxies over cosmic time.
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DECATALDO, DAVIDE. "The Effect of Stellar and Quasar Feedback on the Interstellar Medium: Structure and Lifetime of Molecular Clouds." Doctoral thesis, Scuola Normale Superiore, 2020. http://hdl.handle.net/11384/90712.
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Serrano, Medina Sac Nicte Xiomara [Verfasser]. "Radio emission from massive Young Stellar Objects and their surroundings : Characterization and feedback / Sac Nicte Xiomara Serrano Medina." Bonn : Universitäts- und Landesbibliothek Bonn, 2020. http://d-nb.info/1221668978/34.
Повний текст джерелаКниги з теми "Stellar feedbacks"
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Emerick, Andrew James. Stellar Feedback and Chemical Evolution In Dwarf Galaxies. [publisher not identified], 2019.
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DAEC Workshop (3rd 1992 Observatoire de Paris-Meudon). The feedback of chemical evolution on the stellar content of galaxies: Proceedings of the 3rd DAEC Workshop, Observatoire de Paris/Meudon October 12-16, 1992. Imprimerie de l'Observatoire de Paris, Section Meudon, 1992.
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Hoelscher, Jason A. Art as Information Ecology. Duke University Press, 2021. http://dx.doi.org/10.1215/9781478021681.
Повний текст джерелаАнотація:
In Art as Information Ecology, Jason A. Hoelscher offers not only an information theory of art but an aesthetic theory of information. Applying close readings of the information theories of Claude Shannon and Gilbert Simondon to 1960s American art, Hoelscher proposes that art is information in its aesthetic or indeterminate mode—information oriented less toward answers and resolvability than toward questions, irresolvability, and sustained difference. These irresolvable differences, Hoelscher demonstrates, fuel the richness of aesthetic experience by which viewers glean new information and insight from each encounter with an artwork. In this way, art constitutes information that remains in formation---a difference that makes a difference that keeps on differencing. Considering the works of Frank Stella, Robert Morris, Adrian Piper, the Drop City commune, Eva Hesse, and others, Hoelscher finds that art exists within an information ecology of complex feedback between artwork and artworld that is driven by the unfolding of difference. By charting how information in its aesthetic mode can exist beyond today's strictly quantifiable and monetizable forms, Hoelscher reconceives our understanding of how artworks work and how information operates.
Частини книг з теми "Stellar feedbacks"
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Ristikangas, Vesa, and Tapani Rinne. "Feedback puts wings on development." In Stellar Management Teams. Routledge, 2018. http://dx.doi.org/10.4324/9781351244114-14.
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Letokhov, Vladilen S. "Noncoherent Feedback in Space Masers and Stellar Lasers." In Amazing Light. Springer New York, 1996. http://dx.doi.org/10.1007/978-1-4612-2378-8_41.
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Fender, Rob, and Teo Muñoz-Darias. "The Balance of Power: Accretion and Feedback in Stellar Mass Black Holes." In Astrophysical Black Holes. Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-19416-5_3.
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Bastian, Morten, and Andreas Mühling. "Erste Schritte zur automatisierten Generation von Items in einem webbasierten Tracingsystem." In Die Zukunft des MINT-Lernens – Band 1. Springer Berlin Heidelberg, 2022. http://dx.doi.org/10.1007/978-3-662-66131-4_12.
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ZusammenfassungDer Beitrag stellt die Ergebnisse einer Vorstudie und einer experimentellen Studie (N = 273) in der Sekundarstufe und der Universität im Kontext der Programmierung, genauer der Programmablaufverfolgung (Tracing), vor. Das Ziel ist die automatische Generierung von Items in einem adaptiven Testsystem, die bekannte Fehlvorstellungen sichtbar machen können. Verglichen werden dazu zunächst die empirisch unter Lernenden ermittelten Schwierigkeiten bekannter Items mit den Schwierigkeiten, die aus einem theoretischen Vorhersagemodell abgeleitet werden, sowie mit einem Rating von Experten. Darauf aufbauend werden Items anhand von einfachen Regeln generiert und in einer Hauptstudie deren durch die Regeln vorhergesagte Schwierigkeitsrangfolge empirisch überprüft. Die Ergebnisse zeigen, dass eine solche regelbasierte Generierung von Items vielversprechend ist. Bestimmte Programmkonstrukte sind hinsichtlich ihrer Schwierigkeit auf diese Weise gut klassifizierbar und können so für die automatisierte Itemkonstruktion genutzt werden. Praktisch erlauben solche adaptiven Testverfahren in kurzer Zeit die Diagnose von Fehlvorstellungen, die eine große Hürde in der Programmierausbildung darstellen. Aufgrund der Regeln und des Itemformats ist es darüber hinaus möglich, gezielt Feedback zu den Fehlvorstellungen an die Testerinnen und Tester, oder auch die Lernenden selbst, zu geben.
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"Stellar Feedback." In Star Formation. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813142046_0008.
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Loeb, Abraham, and Steven R. Furlanetto. "Stellar Feedback and Galaxy Formation." In The First Galaxies in the Universe. Princeton University Press, 2013. http://dx.doi.org/10.23943/princeton/9780691144917.003.0006.
Повний текст джерелаАнотація:
This chapter studies radiative, mechanical, and chemical feedback in the earliest gaseous clouds, taking up the thread of discussion in the previous chapter to consider the influences placed on the formation of second-generation stars. While the feedback effects are sufficiently complex that a complete description of them is well beyond the capabilities of present-day computer simulations, the general principles that underlie them are well known. Therefore, the chapter focuses on these principles and then briefly sketches the global picture. Feedback is important in all galaxies, and many of the principles that are discussed in this chapter apply on a much wider scale than just the first stars and galaxies.
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"Chapter Six. Stellar Feedback and Galaxy Formation." In The First Galaxies in the Universe. Princeton University Press, 2013. http://dx.doi.org/10.1515/9781400845606.174.
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Akputu, Oryina Kingsley, and Kingsley Friday Attai. "User Experience Measurement." In Advances in Business Information Systems and Analytics. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-3756-5.ch015.
Повний текст джерелаАнотація:
User experience (UX) measurement has become a powerful component in determining the usability success or failure of products or services that are marketed via e-business channels. Succcess in the e-business does not only depend on building stellar software interfaces but also on competitive receptiveness to customers experience or feedback. Only e-businesses that can effectively measure the UX to forecast and understand the future are able to stay afloat and not get drown in the highly competitive market. The development of various UX metrics and measurement techniques have helped to quantify user feedack but most of these rely on different contextual assumptions. As a result, choosing appropriate UX techniques that match a particular business need becomes difficult for most e-business concerns. This chapter provides an overview of recent UX measurement techniques that are relevant to the e-business settings in the Web 2.0 era. The objective is to elaborate on what tools that have been employed in literature to measure UX and possibly how these can be employed in practice.
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Kirschhock, Eva-Maria, Miriam Grüning, and Miriam Hess. "Mentoring im Praktikum aus der Sicht von Grundschullehramts- studierenden – Wie können nachhaltige Unterrichtsbesprechungen im Praktikum gestaltet werden?" In Nachhaltige Bildung in der Grundschule. Verlag Julius Klinkhardt, 2023. http://dx.doi.org/10.35468/6035-66.
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Praktika in der Lehrer*innenbildung halten eine Vielzahl an Lerngelegenheiten bereit, die jedoch nicht immer bestmöglich genutzt werden. Gerade für einen nachhaltigen Wissens- und Kompetenzerwerb stellt die Begleitung durch die Praktikumslehrperson eine wichtige Einflussgröße dar. Schnebel (2022, S. 19) legt drei zentrale Zielsetzungen für Schulpraktika fest: 1. (Weiter-)entwicklung didaktischer und pädagogisch-psychologischer Kompetenzen; 2. Überprüfung und Reflexion der Berufswahl; 3. Anbahnung der Verantwortungsübernahme typischer Aufgaben von Lehrkräften. Hier ist die Praktikumslehrperson einerseits in der Rolle als Vorbild bzw. Modell, indem Studierende deren Verhaltensweisen im Umgang mit den Schüler*innen oder deren Vorgehen bei der Unterrichtsplanung und -durchführung beobachten. Wichtig ist allerdings, dass Studierende nicht unreflektiert das Verhalten ihrer Praktikumslehrkraft übernehmen. Daher ist es bedeutsam, dass die Praktikumslehrkraft durch angemessenes Feedback und geeignete Impulse Reflexionsprozesse initiiert. Denn Reflexion ermöglicht immer wieder eine Neustrukturierung des eigenen Denkens, was wichtig ist im Umgang mit Unsicherheiten und Herausforderungen im Lehrberuf. Gerade in Unterrichtsvor- und -nachbesprechungen können solche nachhaltigen Reflexionsprozesse unterstützt werden. Daher möchten wir in diesem Beitrag zunächst die wichtige Aufgabe von Praktikumslehrkräften gerade in Bezug auf die Gestaltung von Unterrichtsnachbesprechungen hervorheben, um anschließend anhand einer Studierendenbefragung die Perspektiven Studierender im Grundschullehramt zu deren Erfahrungen und Wünschen dazu aufzuzeigen. (DIPF/Orig.)
Тези доповідей конференцій з теми "Stellar feedbacks"
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Padilla, Nelson D., Claudia Lagos, Michael Strauss, Sebastian Heinz, and Eric Wilcots. "Stellar Disc—Active Nucleus Alignments in the SDSS." In THE MONSTER’S FIERY BREATH: FEEDBACK IN GALAXIES, GROUPS, AND CLUSTERS. AIP, 2009. http://dx.doi.org/10.1063/1.3293009.
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Hueckstaedt, Robert, Daniel Whalen, Thomas McConkie, Daniel J. Whalen, Volker Bromm, and Naoki Yoshida. "Local Radiative Feedback: The Rise of Early Stellar Populations." In THE FIRST STARS AND GALAXIES: CHALLENGES FOR THE NEXT DECADE. AIP, 2010. http://dx.doi.org/10.1063/1.3518869.
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CIARDI, B., and A. FERRARA. "FIR/SUB-MM LINE EMISSION FROM THE FIRST OBJECTS: TESTING THE STELLAR FEEDBACK." In Implications for Galaxy Formation and Evolution. WORLD SCIENTIFIC, 2001. http://dx.doi.org/10.1142/9789812811738_0029.
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Indahl, Briana, Brian Fleming, Dmitry Vorobiev, et al. "Status and mission operations of the SPRITE 12U CubeSat: a probe of star formation feedback from stellar to galactic scales with far-UV imaging spectroscopy." In UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XXIII, edited by Oswald H. Siegmund and Keri Hoadley. SPIE, 2023. http://dx.doi.org/10.1117/12.2677737.
Повний текст джерелаЗвіти організацій з теми "Stellar feedbacks"
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Li, Richard. LegalOne Stellar Accolade 2023 - China. LegalOne Global Limited, 2023. http://dx.doi.org/10.62436/a-1702224947429.
Повний текст джерелаАнотація:
The LegalOne Stellar Accolade is an honour roll serving as an illustrious recognition of the practical prowess and expertise of legal professionals. The evaluation process is rooted in the thorough assessment of commercial projects submitted by the legal professionals. LegalOne’s editorial team reviews each submission, encompassing a broad spectrum of commercial transactions, dispute cases, and intellectual property matters. The declaration of the LegalOne Stellar Accolade winners is based on a composite of factors, include the quality and level of LegalOne Merits ratings awarded to the applicants, supplemented by client feedback and other indicators of professional capability.
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Dudenbostel, Tobias, and David Heckenberg. Bedarfsanalyse Qualifizierungsoffensive. Endbericht an das Bundesministerium für Digitalisierung und Wirtschaftsstandort (BMDW). BMDW - Bundesministerium für Digitalisierung und Wirtschaftsstandort, 2022. http://dx.doi.org/10.22163/fteval.2022.564.
Повний текст джерелаАнотація:
Seit 2011 unterstützt das Bundesministerium für Digitalisierung und Wirtschaftsstandort (BMDW) mit dem Programm Qualifizierungsoffensive bzw. Forschungskompetenzen für die Wirtschaft den systematischen Auf- und Ausbau von Kompetenzen von Unternehmen und ihrer Mitarbeiter*innen in den Bereichen Forschung, Technologie, Entwicklung, Innovation und Digitalisierung. Das Programm wird von der FFG administriert und umfasst heute Konsortialprojekte zwischen Wissenschaft und Wirtschaft von verschiedener Länge und Intensität (Innovationscamp S, M, und Digital Pro Bootcamp) sowie den Digital Skills Scheck. Im März 2022 hat das BMDW Technopolis mit der Durchführung einer Bedarfsanalyse zum Programm beauftragt. Die Studie ist zentral von einer durch das BMF initiierten Änderung in den Rahmenbedingungen des Programms motiviert: durch die neue Förderrichtlinie „Forschungs-, Technologie- und nnovationsrichtlinie – Humanressourcen“ können in Zukunft keine Personalkosten für die an den Schulungen teilnehmende Mitarbeiter*innen von Unternehmen gefördert werden. Damit stellt sich die Frage, was das für die Attraktivität des Programms bzw. der Förderinstrumente bedeutet und wie die Instrumente angepasst werden könnten, sodass Unternehmen weiterhin ihre Mitarbeiter*innen über diese Formate fortbilden. Darüber hinaus beantwortet die Studie Fragen zu Hemmnissen für die Teilnahme, zur thematischen und methodischen Ausgestaltung der Instrumente und präsentiert weiteres Feedback der Unternehmen und anderer Akteure (z.B. wissenschaftliche Einrichtungen, Clusterorganisationen oder regionale Innovationsagenturen).