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Letteratura scientifica selezionata sul tema "Spectral line formation Congresses"

Autore: Grafiati
Pubblicato: 29 luglio 2024
Ultima modifica: 30 luglio 2024

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Articoli di riviste sul tema "Spectral line formation Congresses"

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Paletou, F., e C. Peymirat. "Full non–LTE spectral line formation". Astronomy & Astrophysics 649 (maggio 2021): A165. http://dx.doi.org/10.1051/0004-6361/202040005.

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Radiative transfer out of local thermodynamic equilibrium (NLTE) has been increasingly adressed, mostly numerically, for about six decades now. However, the standard NLTE problem most often refers to the only deviation of the distribution of photons from their equilibrium, that is to say a Planckian distribution. Hereafter we revisit after Oxenius (1986, Kinetic theory of particles and Photons – Theoretical Foundations of non–LTE Plasma Spectroscopy, Springer) the so-called full NLTE problem, which considers coupling and therefore solving self–consistently for deviations from equilibrium distributions of photons as well as for massive particles constituting the atmospheric plasma.
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Oxenius, J., e E. Simonneau. "Kinetic Theory of Spectral Line Formation". Annals of Physics 234, n. 1 (agosto 1994): 60–101. http://dx.doi.org/10.1006/aphy.1994.1074.

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Klevas, J., A. Kučinskas, M. Steffen, E. Caffau e H. G. Ludwig. "Lithium spectral line formation in stellar atmospheres". Astronomy & Astrophysics 586 (febbraio 2016): A156. http://dx.doi.org/10.1051/0004-6361/201526403.

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Peraiah, A., e M. Srinivasa Rao. "Compton broadening effect on spectral line formation". Astrophysics and Space Science 343, n. 1 (18 settembre 2012): 195–211. http://dx.doi.org/10.1007/s10509-012-1233-0.

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5

Nikoghossian, A. G. "Spectral line formation in a mesoturbulent atmosphere". Astrophysics 50, n. 2 (aprile 2007): 175–86. http://dx.doi.org/10.1007/s10511-007-0017-7.

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6

Grec, C., H. Uitenbroek, M. Faurobert e C. Aime. "Measuring line formation depths by cross-spectral analysis". Astronomy and Astrophysics 514 (maggio 2010): A91. http://dx.doi.org/10.1051/0004-6361/200811455.

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Letunov, Andrey Yu, e Valery S. Lisitsa. "Review of Rydberg Spectral Line Formation in Plasmas". Atoms 11, n. 10 (17 ottobre 2023): 133. http://dx.doi.org/10.3390/atoms11100133.

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Abstract (sommario):
The present review is dedicated to the problem of an array of transitions between highly-excited atomic levels. Hydrogen atoms and hydrogen-like ions in plasmas are considered here. The presented methods focus on calculation of spectral line shapes. Fast and simple methods of universal ionic profile calculation for the Hnα (Δn=1) and Hnβ (Δn=2) spectral lines are demonstrated. The universal dipole matrix elements formulas for the Hnα and Hnβ transitions are presented. A fast method for spectral line shape calculations in the presence of an external magnetic field using the formulas for universal dipole matrix elements is proposed. This approach accounts for the Doppler and Stark–Zeeman broadening mechanisms. Ion dynamics effects are treated via the frequency fluctuation model. The accuracy of the presented model is discussed. A comparison of this approach with experimental data and the results of molecular dynamics simulation is demonstrated. The kinetics equation for the populations of highly-excited ionic states is solved in the parabolic representation. The population source associated with dielectronic recombination is considered.
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Albrow, Michael D., e P. L. Cottrell. "Formation Depths of Spectral Lines in Cepheids". International Astronomical Union Colloquium 155 (1995): 373–74. http://dx.doi.org/10.1017/s0252921100037568.

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There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.
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Dravins, Dainis. "Observed and computed spectral line profiles". Symposium - International Astronomical Union 176 (1996): 519–22. http://dx.doi.org/10.1017/s0074180900083534.

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Abstract (sommario):
For the diagnostics of stellar surface structure, studies of “ordinary” line profiles may prove inadequate. However, hydrodynamic models may be constrained by second-order quantities, such as line asymmetries and wavelength shifts (and especially the differential behavior between lines of different excitation potential, ionization stage, and height of formation, as well as by the time dependence).
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10

Ivonina, Liudmila. "The Triumph of Peace: International Congresses and European Society in the Time of Courts and Alliances". ISTORIYA 13, n. 1 (111) (2022): 0. http://dx.doi.org/10.18254/s207987840018801-0.

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The formation of the first state system in Europe took place from the conclusion of the Peace of Westphalia in 1648, as a result of the Thirty Years' War (1618-1648), to the Utrecht (1713) and Rastatt-Baden (1714) Congresses which finished the end of the war of the Spanish Succession. The legal fixation of the Westphallian system was accompanied by its public perception and acceptance. First of all, this was demonstrated by International Congresses, which were not only a common negotiation process, but also a place of representation of the significance and culture of each state. In fact, the European Congress was a carefully designed triumph of peace within the continent, which required considerable funds, was widely covered in the press and glorified in celebrations, paintings, the release of commemorative medals, poetry and even fashion. The article presents the most striking examples of the analysis of the representation forms of Peace Congresses. The author believes that negotiations between states and the conclusion of peace made a significant contribution to the civilization heritage of Europe. The factor of transition from war to peace was the strongest stimulus for the transformation of the government structure in line with the monopolization of power, the development of trade, the banking system, productive forces and culture, which changed people's attitude to their own personality and environment. The publicity of International Congresses can also be considered as incentive for the development of the Law of Nations and as an act of humanitarian diplomacy. Peace Congresses were designed to minimize the heavy legacy of military conflicts in the historical memory.
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Tesi sul tema "Spectral line formation Congresses"

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Gibb, Andrew Gordon. "Spectral line observations of two contrasting molecular clouds : Lynds 1630 and G34.3+0.2". Thesis, University of Kent, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239827.

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2

Bedikoglou, Isidore. "A study of spectral line surveys for four regions related to star formation". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514420.

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Star formation is a process that has been studied extensively during the last decades. With the advent of advanced instruments our knowledge has expanded beyond the point of general descriptions. From simple models of gravitational contraction of spherical clouds we have managed to give more detailed descriptions about the inner processes and the chemistry within the environment of proto stars and young stellar objects. Still there are several issues that have not been fully understood, such as the formation of stars with very large masses, the exact mechanism that generates strong bipolar outflows and the chemical routes through which complex molecules are formed within the young stellar envelopes. A wide field of research is associated with observations of the rotational transitions of molecules in the centimetre and (sub)millimetre ranges. Our study concentrates on the analysis of data from two spectral surveys one in the centimetre and one in the millimetre range. We have performed calculations of column densities and abundances of several species from four different sources of different masses and evolutionary stages. The sample includes two high-mass young stellar objects (AFGL 2591 and lRAS 20126), one low-mass binary system (NGC1333-IRAS 4), and a well known photon dominated region (Orion Bar). For AFGL 2591 temperature and density profiles are developed based on a combination of calculations and non-LTE radiative transfer modelling of spectral lines. The same analysis revealed great abundance enhancements for CH30H, and S02 of factors ≥103 suggesting the existence of a hot core. Related to this is the detection of CH30CH3, the first complex organic molecule detected towards this source. Furthermore, CH30H maps have revealed an unusual ring-like structure which has been explained by a scenario that requires the enhancement of CH30H in outflow regions of shocked gas. The study of the radio recombination lines in combination with radio flux measurements leads to the conclusion that the large radio source in the vicinity of the AFGL 2591 is an ultra compact HII-region associated with a different object in the background. For lRAS 20126 and IRAS 4 the conditions of the outer layers of their envelopes are estimated by non-LTE radiative transfer modelling of mainly centimetre lines. The results are about T≈30K and nH2≈105cm-3 typical in the outer regions of young stellar envelopes. Inverse P-Cygni profiles of H2CO at 14.488GHz, have been detected which imply kinematics of infall within the envelopes of both sources. This suggests that the sources are at an early evolutionary stage. The profile is more prominent towards lRAS 4, which is a complicated system of more than one component. We suggest that motions of infall might exist in outer layers of the surrounding cloud apart from the regions near the stellar components. Finally the maps of the Orion Bar have confirmed the clumpy medium by the detection of two separate clumps in the region. Their masses are estimated to be about IIM®. Based on radio recombination lines the temperature of the Orion nebula has been found to be 9017 K, reflecting a mature HIIregion. The findings of this study will be combined with the JCMT Spectral Legacy Survey, which is currently collecting data from observations in the submillimetre range towards the same sources.
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Lo, Wing-Chi Nadia Physics Faculty of Science UNSW. "A multi-molecular line study of an entire giant molecular cloud". Awarded by:University of New South Wales. Physics, 2009. http://handle.unsw.edu.au/1959.4/44587.

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A unified theory of star formation remains one of the major unsolved issues in astrophysics. Presented here are the results of multi-molecular lines mapping of the entire giant molecular cloud G333, comprised sites of low- and high-mass star forming regions in various evolution stages of star formation. The result shows the spatial distribution of CS, HCO+, HCN and HNC are similar on large scales, while N2H+ seems to trace preferentially the very densest regions, possibly due to the chemical difference, that N2H+ is sensitive to temperature and readily destroyed by CO. Two analysis methods were used to characterise this large set of data cubes: GAUSSCLUMPS and principal component analysis (PCA). We found the clumps are heavily fragmented with a beam filling factor of ~0.2. We found no correlation between clump radius and line width, contradicts to Larson's Law. Possible explanation is the clumps are fragmented and unresolved with the resolution of Mopra beam, thus the decomposed clump radius is blended and no physical properties can be interpreted. PCA of the velocity dimension found no significant differences among CS, HCO+, HNC and C2H line emissions, suggesting these four molecules are `well-mixed' on large scale, possibly by turbulence. PCA of the integrated emission maps separates molecules into low (13CO and C18O) and high (the rest) density tracers, identifies anti-correlation between HCO+ and N2H+ (due to the depletion of CO). The possibility of removing the scanning patterns of the `on-the-fly' mapping with PCA was also explored. The detection of broad thermal SiO from the massive dense cold core G333.125-0.562, along with other collected transitions, suggesting the core will host massive star formation and the SiO emission arises from shocks associated with an outflow in the cold core. Result of the modelling infall with 3D radiative transfer code using the derived physical parameters have successfully reproduce the line profiles. Recent observation of the 3 and 7 mm continuum emission suggestive of warm dust emission rather than free-free emission from HII, further supports the core is in a very young stage of star formation.
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Li, Shanghuo, Junzhi Wang, Zhi-Yu Zhang, Min Fang, Juan Li, Jiangshui Zhang, Junhui Fan, Qingfeng Zhu e Fei Li. "Millimetre spectral line mapping observations towards four massive star-forming H ii regions". OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623847.

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We present spectral line mapping observations towards four massive star-forming regions Cepheus A, DR21S, S76E and G34.26+0.15 - with the IRAM 30-m telescope at the 2 and 3 mm bands. In total, 396 spectral lines from 51 molecules, one helium recombination line, 10 hydrogen recombination lines and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 14(0), 14-13(0), (13)) was detected in G34.26+0.15, as the first detection in massive star-forming regions. We found that c-C3H2 and NH2D show enhancement in shocked regions, as suggested by the evidence of SiO and/or SO emission. The column density and rotational temperature of CH3CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of C-12/C-13 were derived using HC3N and its C-13 isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value (similar to 65). The N-14/N-15 and O-16/O-18 abundance ratios in these sources were also derived using the double isotopic method, which were slightly lower than in the local interstellar medium. Except for Cep A, the S-33/S-34 ratios in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N( DCO+)/N(HCO+) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5 x 10(-5). Our results show that the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage sources. Evidence of shock activity is seen in all stages studied.
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Martinez, Osorio Yeisson Fabian. "Atomic Processes in Stellar Atmospheres : Inelastic Collisions and Effects on Late-type Spectra". Doctoral thesis, Uppsala universitet, Teoretisk astrofysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-249168.

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Chemical abundances as measured from stellar spectral lines are often subject to uncertainties due to lack of accurate data for inelastic collisions, which is needed for non-local thermodynamic equilibrium (non-LTE) modelling. For cool stars, understanding of collision processes with electrons and hydrogen atoms is required to achieve high precision measurements. In this thesis, I have investigated the role of these collisions on the non-LTE formation of Li and Mg spectral lines in late-type stars. In the case of Li, electron impact excitation processes were calculated using the R-matrix with pseudo states method and the results found to agree well with recent calculations using the convergent close-coupling technique. These modern data were employed in non-LTE calculations by updating an existing model atom, which already included modern data for hydrogen collision processes. Our results were compared with calculations using older semi-empirical approximation calculations and only small differences were found: about 0.01 dex (~ 2%) or less in the abundance corrections. We therefore conclude that the influence of uncertainties in the electron collision data on non-LTE calculations is negligible. Indeed, together with the collision data for the charge transfer process Li + H ↔ Li+ + H- now available, and barring the existence of an unknown important collisional process, the collisional data in general is not a source of significant uncertainty in non-LTE Li line formation calculations. In the case of Mg, electron impact excitation processes were again calculated with the Rmatrix with pseudo states method, and used together with recent hydrogen collision calculations to build and test a model atom, without free parameters, for non-LTE modelling. Both electron and hydrogen collision processes, including charge transfer and excitation, are found to be important thermalising agents in various cases. The modelled spectra agree well with observed spectra from benchmark stars in the optical and infrared. The modelling predicts non-LTE abundance corrections ∆A(Mg)NLTE–LTE in dwarfs, both solar metallicity and metal-poor, to be very small (of order 0.01 dex), even smaller than found in previous studies. In giants, corrections vary greatly between lines, but can be as large as 0.4 dex. Results of calculations in a large grid of 1D model atmospheres are presented, and the implications for studies of Mg discussed. The propagation of uncertainties in the inelastic collision data to those in stellar abundances is investigated, and found to lead to small uncertainties, once again typically less than 0.01 dex (2%), although for few stellar models in specific lines (e.g., metal-poor suns, in the 7691 Å line) uncertainties can be as large as 0.03 dex (7%).
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Hindson, Luke Paul. "The G305 star forming complex : a panoramic view of the environment and star formation". Thesis, University of Hertfordshire, 2012. http://hdl.handle.net/2299/9197.

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This thesis presents molecular line and radio continuum observations of the giant molecular cloud (GMC) complex known as G305. The energy input from high-mass stars in the form of powerful winds and ionising radiation is one of the primary feedback mechanisms in GMCs. This feedback is thought to play a dual role both dispersing and destroying the natal environment but also sweeping up and compressing molecular gas and potentially triggering new episodes of star formation. Despite their importance to the evolution of GMCs and galaxies as a whole, the physical processes behind the formation and evolution of high-mass stars remains poorly understood. We therefore set out to obtain wide-field observations of the ionised and molecular environment to study the impact of high-mass stars on the evolution of G305. Observations conducted with the Mopra telescope of the molecular gas traced by NH3 in the (1,1), (2,2) and (3,3) transition and CO (12CO, 13CO and C18O J = 1–0) reveals the reservoir for future star formation in G305 and allows the physical properties and kinematics of the region to be studied. We identify 15 large molecular clouds and 57 smaller molecular clumps towards G305. The physical properties of the molecular gas are consistent with G305 being amongst the most massive a vigorous star forming regions in the Galaxy. We find a total molecular gas mass of 2:5–6:5 105M indicating that there is a large reservoir for future star formation. By considering virial equilibrium within the molecular clumps we discover that only 14% of the molecular clumps in G305 are gravitationally unstable, however these clumps contain > 30% of the molecular mass in G305 suggesting there is scope for considerable future star formation. To study the ionised environment towards G305 we have obtained some of the largest and most detailed wide-area mosaics with the Australia Telescope Compact Array to date. These radio continuum observations were performed simultaneously at 5.5 and 8.8 GHz and by applying two imaging techniques we are able to resolve HII regions from the ultra-compact to classical evolutionary phase. This has allowed high-mass star formation within G305 to be traced over the extent and lifetime of the complex. We discover that more than half of the observable total ionising flux in G305 is associated with embedded high-mass star formation around the periphery of a central cavity that has been driven into the molecular gas by a cluster of optically visible massive stars. By considering the contribution of embedded and visible massive stars to the observed radio continuum we suggest that more than 45 massive stars exist within G305. Combination of these two studies and recent and ongoing star formation provides the most in depth view of G305 to date and allows the star formation history and impact of high-mass stars to be investigated. We find compelling morphological evidence that suggests triggering is responsible for at least some of the observed high-mass star formation and construct a star formation history for the region.
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Pacheco-Vazquez, Susana. "Unbiased Spectral Survey towards the intermediate-mass Class 0 protostar Cep E-mm". Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY066/document.

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Les protoétoiles de masse intermédiaire (IM) (2 ≤ M* ≤ 8 Msun) sont le lien entre les étoiles de faible et haute masse car elles couvrent également un intervalle intermédiaire de luminosités, de densités et de températures [Fuente et al., 2012]. Même si les « IM-YSOs » jouent un rôle important dans l'étude de la formation des étoiles, on a très peu de connaissances sur la formation et l'évolution des premières étapes des protoétoiles de masse intermédiaire. Les études systématiques spectrales sont un outil puissant pour caractériser la composition chimique d'un objet astrophysique, et la seule façon d'obtenir un recensement complet des espèces chimiques. Une étude spectrale fournit également des lignes multiples de la même molécule, donnant la possibilité d'une analyse multifréquences ainsi que d'une modélisation. En outre, grâce aux profils des raies, nous pouvons obtenir des informations sur la cinématique, et identifier les structures au long de la ligne de vue, en tant que sources multiples, des jets ou des cavités, par exemple, [Caux et al., 2011]. Les phénomènes d'éjection (jets, des vents et des « outflows » bipolaires moléculaires), sont une phase inhérente au processus de formation d'étoiles observées dans les YSOs de toutes masses dans des longueurs d'onde millimétriques. Cependant, il n'y a pas d'études systématiques dans l'intervalle de masse intermédiaire comme dans le cas des protoétoiles de faible et haute masse. Compte tenu de l'absence d'une étude systématique de la partie mm/submillimétrique dans le spectre des protoétoiles de masse intermédiaire, au cours de ma thèse, j'ai mené une étude systématique spectrale vers la protoétoile de masse intermédiaire de classe 0 Cep E et de son « outflow » moléculaire
Intermediate-mass (IM) protostars (2 ≤ M∗ ≤8 Msun) are the link between low and the high mass stars as they cover also an intermediate range of luminosities, densities and temperatures [Fuente et al., 2012]. Even though the IM-YSOs are important in the study of star formation, very little is known about the formation and first evolutionary stages of IM protostars. Unbiased spectral surveys are a powerful tool to characterize the chemical composition of an astrophysical object, and the only way to obtain a complete census of the chemical species. A spectral survey provides also multiple lines from the same molecule, giving the possibility of a multi-frequency analysis and modeling. Also, through line profiles, we can obtain kinematic information, and identify structures along the line of sight, as multiple sources, outflows, jets or cavities, e.g. [Caux et al., 2011]. The outflow phenomena (jets, winds and bipolar molecular outflows), are an inherent phase in the process of star formation observed in YSOs of all range of masses at millimeter wavelengths. However, there are not systematic studies in IM range as in the case of of low- and high-mass protostars. Given the lack of a systematic study of the mm/submm spectrum of IM protostars, during my thesis I carried out an unbiased spectral survey towards IM Class 0 Cep E protostar and its molecular outflow
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Collet, Remo. "On the Chemical Composition of Metal-Poor Stars : Impact of Stellar Granulation and Departures from Local Thermodynamic Equilibrium on the Formation of Spectral Lines". Doctoral thesis, Uppsala University, Department of Astronomy and Space Physics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7121.

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The information about the chemical compositions of stars is encoded in their spectra. Accurate determinations of these compositions are crucial for our understanding of stellar nucleosynthesis and Galactic chemical evolution. The determination of elemental abundances in stars requires models for the stellar atmospheres and the processes of line formation. Nearly all spectroscopic analyses of late-type stars carried out today are based on one-dimensional (1D), hydrostatic model atmospheres and on the assumption of local thermodynamic equilibrium (LTE). This approach can lead to large systematic errors in the predicted stellar atmospheric structures and line-strengths, and, hence, in the derived stellar abundances. In this thesis, examples of departures from LTE and from hydrostatic equilibrium are explored. The effects of background line opacities (line-blocking) due to atomic lines on the statistical equilibrium of Fe are investigated in late-type stars. Accounting for this line opacity is important at solar metallicity, where line-blocking significantly reduces the rates of radiatively induced ionizations of Fe. On the contrary, the effects of line-blocking in metal-poor stars are insignificant. In metal-poor stars, the dominant uncertainty in the statistical equilibrium of Fe is the treatment of inelastic H+Fe collisions. Substantial departures of Fe abundances from LTE are found at low metallicities: about 0.3 dex with efficient H+Fe collisions and about 0.5 dex without. The impact of three-dimensional (3D) hydrodynamical model atmospheres on line formation in red giant stars is also investigated. Inhomogeneities and correlated velocity fields in 3D models and differences between the mean 3D stratifications and corresponding 1D model atmospheres can significantly affect the predicted line strengths and derived abundances, in particular at very low metallicities. In LTE, the differences between 3D and 1D abundances of C, N, and O derived from CH, NH, and OH weak low-excitation lines are in the range -0.5 dex to -1.0 dex at [Fe/H]=-3. Large negative corrections (about -0.8 dex) are also found in LTE for weak low-excitation neutral Fe lines. We also investigate the impact of 3D hydrodynamical model stellar atmospheres on the determination of elemental abundances in the carbon-rich, hyper iron-poor stars HE 0107-5240 and HE 1327-2326. The lower temperatures of the line-forming regions of the 3D models compared with 1D models cause changes in the predicted spectral line strengths. In particular we find the 3D abundances of C, N, and O to be lower by about -0.8 dex (or more) than estimated from a 1D analysis. The 3D abundance of Fe is decreased but only by -0.2 dex. Departures from LTE for Fe might actually be very large for these stars and dominate over the effects due to granulation.

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Benredjem, Djamel. "Etude théorique du déplacement des raies spectrales par effet de polarisation dans les plasmas denses : cas des raies de l'hélium hydrogenoïde". Paris 6, 1986. http://www.theses.fr/1986PA066016.

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Le déplacement des raies de l'hélium hydrogenoïde émises dans les plasmas denses a été calculé en considérant l'effet des électrons libres et celui des ions perturbateurs sur l'émetteur. Le premier, déterminé par une méthode de potentiel auto-consistant, induit un déplacement vers le rouge alors que le second, calcule par perturbation, décale les raies vers le bleu. Deux méthodes de calcul de cette grandeur ont été développées : l'une permet d'évaluer le déplacement comme moment spectral du profil complet; l'autre, plus simple, séparé les deux contributions et peut s'appliquer à des états très excités. Les résultats théoriques obtenus sont en accord quantitatif avec les expériences les plus récentes.
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García, Pérez Ana Elia. "On the Abundances of Li, Be and O in Metal-Poor Stars in the Galaxy". Doctoral thesis, Uppsala University, The Uppsala Astronomical Observatory, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4814.

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Stellar atmospheres constitute excellent environments to study the chemical evolution of our Galaxy. The chemical composition of these atmospheres reflects the composition of the gas from where these stars were born. As the Galaxy evolves, the composition of the gas changes from being primordial (Big-Bang nucleosynthesis) to being enriched in heavy elements (stellar and interstellar nucleosynthesis). The abundances of fragile chemical elements can be affected by stellar mixing processes. Precise lithium, beryllium and oxygen abundance determinations in old stars are presented in this thesis. These determinations are based on the analysis of the observed spectra of a sample of thirteen metal-poor subgiant stars. According to stellar mixing theories, these stars are in a stellar evolutionary stage in which mixing by convection is expected. Abundances of fragile elements like lithium and beryllium are thus expected to be affected by such mixing processes. As a consequence of this, the abundances of these elements are discussed in a dilution context. Lithium and beryllium abundances are compared with the abundances of stars with similar characteristics but in a less evolved stellar phase so that mixing processes have not acted yet. As expected, our abundances seem to be depleted following reasonably well the standard predictions. Stellar abundances of oxygen should give an estimate of the oxygen contribution of core-collapse supernovae to the interstellar medium. However, there is poor agreement among the abundances determined from different atomic or molecular indicators in general. Abundances coming from three different indicators are compared in this thesis. The abundances determined from the O I infrared triplet lines at 777.1-5 nm give the poorest agreement among the three indicators. The abundances based on OH ultraviolet lines around 310 nm are lower for the subgiants in comparison with previous studies of main-sequence stars, becoming even lower than values based on the O I forbidden line at 630.03 nm. Still the most reliable indicator appears to be the O I forbidden line which suggests a plateau-like or only slowly increasing [O/Fe] towards lower [Fe/H]. In addition, the line formation of the Be II ultraviolet resonance lines at 313.0-1 nm, commonly used for abundance determinations purposes, is investigated under non-local thermodynamic equilibrium. We find that the common assumption of local thermodynamic equilibrium typically gives systematic errors of about 0.1 dex.

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Libri sul tema "Spectral line formation Congresses"

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International, Conference on Spectral Line Shapes (14th 1998 State College Pennsylvania). Spectral line shapes. Woodbury, New York: American Institute of Physics, 1999.

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Marco, Zoppi, e Ulivi Lorenzo, a cura di. Spectral line shapes. Woodbury, New York: American Institute of Physics, 1997.

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Spain) International Conference on Spectral Line Shapes (19th 2008 Valladolid. Spectral line shapes: 19th International Conference on Spectral Line Shapes, Valladolid, Spain, 15-20 June 2008. A cura di Gigosos Marco A e González, Manuel A. (Manuel Angel). Melville, N.Y: American Institute of Physics, 2008.

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Ala.) International Conference on Spectral Line Shapes (18th 2006 Auburn. Spectral line shapes: 18th International Conference on Spectral Line Shapes, Auburn, Alabama, 4-9 June 2006. A cura di Oks, E. A. (Evgeniĭ Aleksandrovich), Pindzola M. S e American Institute of Physics. Melville, N.Y: American Institute of Physics, 2006.

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International Conference on Spectral Line Shapes (12th 1994 Toronto, Ont.). Spectral line shapes.: 12th ICSLS, Toronto, Canada, June 1990. A cura di May A. David, Drummond J. R e Oks E. A. New York: American Institute of Physics, 1995.

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Serbian, Conference on Spectral Line Shapes in Astrophysics (6th 2007 Sremski Karlovci Serbia). Spectral line shapes in astrophysics: VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), Sremski Karlovci, Serbia, 11-15 June 2007. Melville, N.Y: American Institute of Physics, 2007.

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Serbian, Conference on Spectral Line Shapes in Astrophysics (6th 2007 Sremski Karlovci Serbia). Spectral line shapes in astrophysics: VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), Sremski Karlovci, Serbia, 11-15 June 2007. Melville, N.Y: American Institute of Physics, 2007.

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8

Serbian Conference on Spectral Line Shapes in Astrophysics (6th 2007 Sremski Karlovci, Serbia). Spectral line shapes in astrophysics: VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), Sremski Karlovci, Serbia, 11-15 June 2007. A cura di Popović Luka Č, Dimitrijević Milan S e Serbia Ministarstvo nauke. Melville, N.Y: American Institute of Physics, 2007.

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Č, Popović Luka, Dimitrijević Milan S e Serbia Ministarstvo nauke, a cura di. Spectral line shapes in astrophysics: VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), Sremski Karlovci, Serbia, 11-15 June 2007. Melville, N.Y: American Institute of Physics, 2007.

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10

International, Conference on Spectral Line Shapes (15th 2000 Berlin Germany). Spectral line shapes: 15th ICSLS, Berlin, Germany, 10-14 July 2000. Melville, New York: American Institute of Physics, 2001.

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Più fonti

Capitoli di libri sul tema "Spectral line formation Congresses"

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Maciel, Walter J. "Spectral Line Formation". In Astrophysics of the Interstellar Medium, 33–51. New York, NY: Springer New York, 2012. http://dx.doi.org/10.1007/978-1-4614-3767-3_3.

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Hack, M. "Observational Problems in Spectral Line Formation". In Progress in Stellar Spectral Line Formation Theory, 265–77. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_22.

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Jaeglé, P., G. Jamelot e A. Carillon. "Line Formation in Laboratory Plasmas". In Progress in Stellar Spectral Line Formation Theory, 239–63. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_21.

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Nordlund, Å. "NLTE Spectral Line Formation in Three Dimensions". In Stellar Atmospheres: Beyond Classical Models, 61–68. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3554-2_7.

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Oxenius, J. "Kinetic Aspects of Redistribution in Spectral Lines". In Progress in Stellar Spectral Line Formation Theory, 59–71. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_3.

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Beckman, John E. "A Review of Line Formation in Molecular Clouds". In Progress in Stellar Spectral Line Formation Theory, 389–405. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_32.

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Kunasz, P. B. "The Theory of Line Transfer in Expanding Atmospheres". In Progress in Stellar Spectral Line Formation Theory, 319–33. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_25.

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Ferrero, R. Freire. "Some Comments Upon the Line Emission Profile Ψν". In Progress in Stellar Spectral Line Formation Theory, 101–8. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_6.

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Linsky, Jeffrey L. "Observed and Computed Stellar Line Profiles: The Roles Played by Partial Redistribution, Geometrical Extent and Expansion". In Progress in Stellar Spectral Line Formation Theory, 1–26. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_1.

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Heinzel, Petr, e Ivan Hubený. "Partial Redistribution Interlocking in the Solar Chromosphere". In Progress in Stellar Spectral Line Formation Theory, 137–42. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-009-5372-7_10.

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Atti di convegni sul tema "Spectral line formation Congresses"

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Dulieu, Olivier. "Ultracold Molecules: Formation, Detection". In SPECTRAL LINE SHAPES. AIP, 2002. http://dx.doi.org/10.1063/1.1525491.

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Pichler, Goran. "Formation and Detection of Ultracold Molecules". In SPECTRAL LINE SHAPES. AIP, 2002. http://dx.doi.org/10.1063/1.1525490.

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Yurovsky, V. A. "Formation of a molecular Bose-Einstein condensate and an entangled atomic gas by time-dependent Feshbach resonance". In SPECTRAL LINE SHAPES. AIP, 2002. http://dx.doi.org/10.1063/1.1525489.

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Rosato, J., John Lewis e Adriana Predoi-Cross. "Modeling of Coherence Effects on Spectral Line Formation Using the Quantum Phase Space Formalism". In 20TH INTERNATIONAL CONFERENCE ON SPECTRAL LINE SHAPES. AIP, 2010. http://dx.doi.org/10.1063/1.3517586.

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Kewley, L. J. "Emission Line Diagnostics of Star Formation: Nearby and at High Redshift". In THE SPECTRAL ENERGY DISTRIBUTIONS OF GAS-RICH GALAXIES: Confronting Models with Data; International Workshop. AIP, 2005. http://dx.doi.org/10.1063/1.1913915.

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Kuzmanovska, Olgica. "Numerical methods for solution of spectral line formation problems in the stellar atmospheres". In 10th Jubilee International Conference of the Balkan Physical Union. Author(s), 2019. http://dx.doi.org/10.1063/1.5091215.

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Luz, A. M. G., D. Balint e K. Nikbin. "A Multiscale NDT System for Damage Detection in Thermal Barrier Coatings". In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-10694.

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Abstract (sommario):
Progress in aero-engines and land-based gas turbines is continuously linked with a rise of the operating temperature. TBCs are multilayered structures which function together to effectively lower the temperature of its load-bearing superalloy substrate while simultaneously providing oxidation protection against high temperature combustion environments during operation. They typically comprise of a ceramic top coat for thermal insulation and a metallic bond coat that provides oxidation/corrosion resistance and enhances the adhesion of the YSZ to the superalloy substrate. Due to high-temperature oxidation of the bond coat, a thermally grown oxide (TGO) scale of continuous Al2O3 is formed between the ceramic top coat and the bond coat. The formation and growth of the TGO increases the mismatch of thermal expansion coefficients among the multilayered TBC and induce high thermal stresses leading to spallation of the YSZ coat from the underlying metal. Hence, nondestructive diagnostic tools that could reliably probe the subsurface damage state of TBCs are essential to take full advantage of these systems. In this contribution, a new concept of multiscale NDT system is presented. The instrument uses a combination of imaging-based methods with photoluminescence piezospectroscopy, a laser-based method. Imaging-based methods like mid-infrared reflectance, laser optical backscatter and infrared tomography were used to predict the overall lifetime of the coated component. When TBCs approach the end of life, micro-crack nucleation and propagation at the top coat/bond coat interface increases the amount of reflected light. This rise in reflectance was correlated with the lifetime of the component using a neural network that merges the mean and standard deviation value of the gray level. Photoluminescence piezospectroscopy was subsequently used to give information about the structural integrity of the hot spots identified in the image analysis. This laser-based technique measures in-situ the residual stress in the TGO at room temperature. Damage leads to a relaxation of the local stress which is in turn reflected in the luminescence spectrum shape. However, presently there is no agreement on the best spectral parameters that should be used as a measure of the damage accumulation in the coatings. Therefore, the evolution of luminescence spectrum from as-manufactured to critically damaged TBCs was determined using the finite element method. This approach helped to identify the most suitable spectral parameters for damage detection, improving the reliability of photoluminescence piezospectroscopy as a failure assessment tool for TBCs.
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Hayes, John M., Wook Hyun Kim e Gerald J. Small. "Spectral Hole Burning In Hyperquenched Films". In Spectral Hole-Burning and Luminescence Line Narrowing: Science and Applications. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/shbl.1992.tub9.

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Abstract (sommario):
An apparatus for the deposition of doped, thin, amorphous films has been developed. This apparatus is based on the hyperquenching technique of Mayer (1). In this technique aqueous aerosol, i.e. water clusters, is expanded through an orifice and deposited onto a cryoplate. In Mayer’s work the aerosol was produced by an ultrasonic nebulizer and transferred with a carrier gas through an aperture and then onto the cryoplate. In our apparatus the aerosol is formed and deposited from a thermospray nozzle source (2). Use of the thermospray nozzle permits formation of films uncontaminated by condensation of a carrier gas and also permits some control of the size of clusters in the aerosol by control of the temperature differential along the source. An important point is that with this hyperquenching technique, vitrification occurs directly from the liquid state, thus facilitating the inclusion of dopants into the film.
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Horie, Kazuyuki, Norio Murase e Makoto Ikemoto. "Wavelength Dependence of Photochemical Hole-Burning Efficiency and Vibronic Structure in an Absorption Band". In Spectral Hole-Burning and Luminescence Line Narrowing: Science and Applications. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/shbl.1992.fa2.

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Photochemical hole-burning(PHB) is a good tool for understanding the dynamics of host polymers as well as for realizing a high performance optical storage. The quantum efficiency for persistent hole formation, ϕ, is one of the essential parameters for the PHB phenomenon. If one is aware of some kinds of application, its value is preferable to be large. This is why the quantum efficiencies for several series of substances are measured and the efforts to find out the dominant factor for controlling these values are continued.1) As ever, these values are measured near the peaks of the lowest energy absorption bands. However, we noticed recently very large difference in quantum efficiencies of hole formation, ϕ, between the cases when the hole is burnt on the higher frequency slope or on the lower frequency slope of the lowest energy inhomogeneous absorption peak in the Q band of free base tetraphenylporphin derivatives.2) We also found out the wavelength dependences of the formation rate of satellite holes, which originate from the vibronic excitations of the dye molecules accompanied by the electronic excitation. These facts suggest that the lowest energy inhomogeneous absorption band is actually composed of several kinds of vibronic dye transitions, and the 0-0 absorption component is one of the portion of this absorption band.
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Horie, Kazuyuki. "New Mechanisms and New Systems of Hole Formation in Spectral Hole Burning". In Spectral Hole-Burning and Related Spectroscopies: Science and Applications. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/shbs.1994.thf1.

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A variety of studies on persistent spectral hole burning (PSHB) have been carried out for the last twenty years [1-4], since the discovery of this phenomenon in 1974. The elucidation of electron-phonon interaction, the nature of a zero-phonon line and spectral diffusion in PSHB have been studied intensively together with the research aiming at its possible applicability to ultra-high density optical storage. However, as for the PSHB materials, most of the works have been carried out with porphyrins, phthalocyanines, and quinizarin including their derivatives, several organic dyes, samarium and some other inorganic ions. The number of molecules reported to show hole formation so far is restricted compared to a wide variety of chemical structure of organic molecules. This would be because it is usually thought that for the hole formation the existence of a zero-phonon line in guest molecules for SHB should be accompanied by the occurrence of some photochemical reaction of the guest molecules. A well-known exception on this point is the so-called non-photochemical hole burning (NPHB) [4]. Recently triplet-triplet energy transfer of guest molecule to a host photo-reactive matrix has been reported to be a new family [5] of PSHB systems with new mechanism.
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Rapporti di organizzazioni sul tema "Spectral line formation Congresses"

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Heinola, Kalle. Atomic Data for Vapour Shielding in Fusion Devices. IAEA Nuclear Data Section, maggio 2019. http://dx.doi.org/10.61092/iaea.zzjz-hsb9.

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The First Research Coordination Meeting of the Coordinated Research Project on Atomic Data for Vapour Shielding in Fusion Devices was held at the IAEA Headquarters in Vienna on 13 – 15 March 2019. Nine experts representing nine research institutes globally (Australia, China, India, Italy, Netherlands, North Macedonia, Spain, Syria, USA) in the field of atomic collisional physics and vapour formation for magnetic confinement fusion devices met together with the IAEA staff. The participants were theorists and modellers of plasma and vapour particle collisional processes, experimentalists of spectral line properties, and vapour formation and spectral analyses. They described their research background, available experimental methodologies and theories applied in various computational tools. Open issues related to elemental particles formed during vapour evolution and the particle interaction processes were discussed and plans for coordinated research to be performed during the project were made. The proceedings of the meeting are summarized in this report.
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Heinola, K. Summary Report of the Second Research Coordination Meeting on Atomic Data for Vapour Shielding in Fusion Devices. IAEA Nuclear Data Section, febbraio 2021. http://dx.doi.org/10.61092/iaea.gd9j-0nr6.

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Abstract (sommario):
The Second Research Coordination Meeting of the Coordinated Research Project on Atomic Data for Vapour Shielding in Fusion Devices was held as a virtual meeting on 7 – 9 October 2020. Eight experts representing eight research institutes globally (Australia, China, India, Netherlands, Spain, Syria, USA) in the field of atomic collisional physics and vapour formation for magnetic confinement fusion devices met together with the IAEA staff. Participants were theorists and modellers of plasma and vapour par-ticle collisional processes, experimentalists of spectral line properties, and vapour formation and spec-tral analyses. They described their research background, available experimental methodologies and the-ories applied in various computational tools as well as the results obtained. Open issues related to ele-mental particles formed during vapour evolution and the particle interaction processes were discussed and plans for coordinated research to be performed during the project were made. The proceedings of the meeting are summarized in this report.
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