Literatura académica sobre el tema "Spiral bulges"
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Artículos de revistas sobre el tema "Spiral bulges"
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Thomas, Daniel y Roger L. Davies. "Rejuvenation of spiral bulges". Proceedings of the International Astronomical Union 3, S245 (julio de 2007): 289–92. http://dx.doi.org/10.1017/s1743921308017936.
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AbstractWe seek to understand whether the stellar populations of galactic bulges show evidence of secular evolution triggered by the presence of the disc. To this end we re-analyse the sample of Proctor & Sansom (2002), deriving stellar population ages and element abundances from absorption line indices as functions of central velocity dispersion and Hubble type. In agreement with other studies in the literature, we find that bulges have relatively low luminosity weighted ages, the lowest age derived being 1.3 Gyr. Hence bulges are not generally old, but actually rejuvenated systems. We discuss evidence that this might be true also for the bulge of the Milky Way. The smallest bulges are the youngest with the lowest α/Fe ratios indicating the presence of significant star formation events involving 10 − 30 per cent of their total mass in the past 1 − 2 Gyr. No significant correlations of the stellar population parameters with Hubble Type are found. We show that the above relationships with σ coincide perfectly with those of early-type galaxies. At a given velocity dispersion, bulges and elliptical galaxies are indistinguishable as far as their stellar populations are concerned. These results favour an inside-out formation scenario and indicate that the discs in spiral galaxies of Hubble types Sbc and earlier cannot have a significant influence on the evolution of the stellar populations in the bulge component. The phenomenon of pseudobulge formation must be restricted to spirals of types later than Sbc.
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Kumar, Ankit, Mousumi Das y Sandeep Kumar Kataria. "Galaxy flybys: evolution of the bulge, disc, and spiral arms". Monthly Notices of the Royal Astronomical Society 506, n.º 1 (22 de junio de 2021): 98–114. http://dx.doi.org/10.1093/mnras/stab1742.
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ABSTRACT Galaxy flybys are as common as mergers in low-redshift Universe and are important for galaxy evolution as they involve the exchange of significant amounts of mass and energy. In this study, we investigate the effect of minor flybys on the bulges, discs, and spiral arms of Milky Way mass galaxies for two types of bulges – classical bulges and boxy/peanut pseudo-bulges. Our N-body simulations comprise of two disc galaxies of mass ratios 10:1 and 5:1, where the discs of the galaxies lie in their orbital plane and the pericentre distance is varied. We performed photometric and kinematic bulge–disc decomposition at regular time-steps and traced the evolution of the disc size, spiral structure, bulge sersic index, bulge mass, and bulge angular momentum. Our results show that the main effect on the discs is disc thickening, which is seen as the increase in the ratio of disc scale height to scale radius. The strength of the spiral structure A2/A0 shows small oscillations about the mean time-varying amplitude in the pseudo-bulge host galaxies. The flyby has no significant effect on non-rotating classical bulge, which shows that these bulges are extremely stable in galaxy interactions. However, the pseudo-bulges become dynamically hotter in flybys indicating that flybys may play an important role in accelerating the rate of secular evolution in disc galaxies. This effect on pseudo-bulges is a result of their rotating nature as part of the bar. Also, flybys do not affect the time and strength of bar buckling.
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Kim, Eunbin, Sungsoo S. Kim, Yun-Young Choi, Gwang-Ho Lee, Richard de Grijs, Myung Gyoon Lee y Ho Seong Hwang. "Nuclear starburst activity induced by elongated bulges in spiral galaxies". Monthly Notices of the Royal Astronomical Society 479, n.º 1 (5 de junio de 2018): 562–69. http://dx.doi.org/10.1093/mnras/sty1451.
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ABSTRACT We study the effects of bulge elongation on the star formation activity in the centres of spiral galaxies using the data from the Sloan Digital Sky Survey Data Release 7. We construct a volume-limited sample of face-on spiral galaxies with Mr < −19.5 mag at 0.02 ≤ $z$ < 0.055 by excluding barred galaxies, where the aperture of the SDSS spectroscopic fibre covers the bulges of the galaxies. We adopt the ellipticity of bulges measured by Simard et al., who performed two-dimensional bulge + disc decompositions using the SDSS images of galaxies, and identify nuclear starbursts using the fibre specific star formation rates derived from the SDSS spectra. We find a statistically significant correlation between bulge elongation and nuclear starbursts in the sense that the fraction of nuclear starbursts increases with bulge elongation. This correlation is more prominent for fainter and redder galaxies, which exhibit higher ratios of elongated bulges. We find no significant environmental dependence of the correlation between bulge elongation and nuclear starbursts. These results suggest that non-axisymmetric bulges can efficiently feed the gas into the centre of galaxies to trigger nuclear starburst activity.
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Richer, Michael G. y Marshall L. McCall. "Several evolutionary channels for bright planetary nebulae". Proceedings of the International Astronomical Union 11, S317 (agosto de 2015): 344–45. http://dx.doi.org/10.1017/s1743921315008832.
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AbstractThe populations of bright planetary nebulae in the discs of spirals appear to differ in their spectral properties from those in ellipticals and the bulges of spirals. The bright planetary nebulae from the bulge of the Milky Way are entirely compatible with those observed in the discs of spiral galaxies. The similarity might be explained if the bulge of the Milky Way evolved secularly from the disc, in which case the bulge should be regarded as a pseudo-bulge.
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MacArthur, Lauren A., Richard S. Ellis y Tommaso Treu. "The fundamental plane of bulges at intermediate redshift". Proceedings of the International Astronomical Union 3, S245 (julio de 2007): 443–46. http://dx.doi.org/10.1017/s1743921308018322.
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AbstractWe report on a new study aimed at understanding the diversity and evolutionary properties of distant galactic bulges in the context of well-established trends for pure spheroidal galaxies. Bulges have been isolated for a sample of 137 spiral galaxies in the GOODS fields within the redshift range 0.1 < z < 1.2. Using proven photometric techniques we determine for each galaxy the characteristic parameters (size, surface brightness, profile shape) in the 4 GOODS-ACS imaging bands of both the disk and bulge components. Using the DEIMOS spectrograph on Keck, precision stellar velocity dispersions were secured for a sizeable fraction of the bulges. This has enabled us to compare the Fundamental Plane of our distant bulges with that of field spheroidal galaxies in a similar redshift range. Bulges in spiral galaxies with a bulge-to-total luminosity ratio (B/T) > 0.2 show very similar patterns of evolution to those seen for low luminosity spheroidals. To first order, their recent mass assembly histories are equivalent.
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Bureau, M. y K. C. Freeman. "The Nature of Boxy/Peanut Spiral Galaxies: Overview and New Results". Publications of the Astronomical Society of Australia 14, n.º 2 (1997): 146–58. http://dx.doi.org/10.1071/as97146.
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AbstractThe formation mechanism of boxy/peanut-shaped bulges in spiral galaxies has been a problem for many years. We briefly review here the possible formation scenarios for boxy/peanut bulges, concentrating on both the bar-buckling and accretion hypotheses, and then describe an observational program aimed at testing those various theories and studying the vertical structure of edge-on bars. Our program includes optical long-slit spectroscopy, Hiline-imaging, near-infrared imaging, and multi-band optical imaging. New spectroscopic results (both optical and Hi) are presented on seven galaxies, including five boxy/peanut-bulge spirals. Based on Kuijken & Merrifield's (1995) idea for detecting edge-on bars, we argue that these observations constitute a strong case in favour of the bar-buckling mechanism for the formation of boxy/peanut-shaped bulges, but they also raise many questions and prompt for more detailed modelling to be made. The implications of the observations concerning the determination of rotation curves and of the physical conditions in bulges are also discussed.
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Mengistu, Petra y Karen L. Masters. "Mass and Color Dependence of the Hubble Spiral Sequence". Research Notes of the AAS 7, n.º 3 (3 de marzo de 2023): 35. http://dx.doi.org/10.3847/2515-5172/acc032.
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Abstract In the classic Hubble spiral sequence, arm windiness correlates with bulge size; Sa type spiral galaxies with larger bulges also have the most tightly wound spirals. Exceptions to this have long been known, and in recent work using Galaxy Zoo morphologies no strong correlation was seen in a volume limited sample. In this Research Note, we explore the impact of galaxy mass and integrated color upon this correlation in the Galaxy Zoo sample, finding that bluer and lower mass spirals show the “expected” correlation; however, it becomes slightly negative for redder and/or more massive spiral galaxies.
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Laurikainen, E., H. Salo, R. Buta y J. H. Knapen. "Overview of the Near-IR S0 Galaxy Survey (NIRS0S)". Advances in Astronomy 2011 (2011): 1–17. http://dx.doi.org/10.1155/2011/516739.
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An overview of the results of the near-IR S0 galaxy survey (NIRS0S) is presented. NIRS0S is a magnitude- (mB⩽12.5 mag) and inclination- (<65∘) limited sample of ̃200 nearby galaxies, mainly S0s, but includes also Sa and E galaxies. It uses deepKs-band images, typically reaching a surface brightness of 23.5 mag arcsec−2. Detailed visual and photometric classifications were made, for the first time coding also the lenses in a systematic manner. As a comparison sample, a similar sized spiral galaxy sample with similar image quality was used. Based on our analysis, the Hubble sequence was revisited: following the early idea by van den Bergh we suggested that the S0s are spread throughout the Hubble sequence in parallel tuning forks as spirals (S0a, S0b, S0c, etc.). This is evidenced by our improved bulge-to-total (B/T) flux ratios in the S0s, reaching small values typical to late-type spirals. The properties of bulges and disks in S0s were found to be similar to those in spirals and, also, the masses and scale parameters of the bulges and disks to be coupled. It was estimated that the spiral bulges brighter than −20 mag inK-band are massive enough to be converted into the bulges of S0s merely by star formation. Bars were found to be fairly robust both in S0s and spirals, but, inspite of that, bars might evolve significantly within the Hubble sequence.
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MacArthur, Lauren A., J. Jesús González, Stéphane Courteau y Michael McDonald. "Stellar Populations and Kinematics in Spiral Galaxies". Proceedings of the International Astronomical Union 5, S262 (agosto de 2009): 172–75. http://dx.doi.org/10.1017/s1743921310002735.
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AbstractWe present a detailed study of the stellar populations (SPs) and kinematics of the bulge and inner disk regions of nearby spiral galaxies (Sa-Sd) based on deep long-slit Gemini/GMOS data. We find that the SPs of spiral galaxies are not well matched by single episodes of star formation; representative SPs must involve average SP values integrated over the star formation history (SFH) of the galaxy, such as those derived from the “full population synthesis” method used here. Our spiral bulges follow the same correlations of increasing light-weighted age and metallicity with central velocity dispersion as those of elliptical galaxies and early-type bulges found in other studies, but when SFHs more complex and realistic than a single burst are invoked, the trend with age is shallower and its scatter much reduced. In a mass-weighted context, all bulges are predominantly composed of old and metal-rich SPs. Bulge formation appears to be dominated by early processes that are common to all spheroids, whether they currently reside in disks or not. While monolithic collapse cannot be ruled out in some cases, merging must be invoked to explain the SP gradients in most bulges. Further bulge growth via secular processes, or “rejuvenated” star formation, generally contributes minimally to the stellar mass budget. We also demonstrate how the combination of our full population synthesis modeling of high-quality optical spectra of integrated SPs along with optical-NIR broad-band imaging can single out potential model weaknesses and help determine the reliability of the inferred SFHs.
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Pastrav, Bogdan A. "On the scaling relations of bulges and early-type galaxies". Monthly Notices of the Royal Astronomical Society 506, n.º 1 (21 de junio de 2021): 452–67. http://dx.doi.org/10.1093/mnras/stab1746.
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ABSTRACT Following from our recent work, we present here a detailed structural analysis of a representative sample of nearby spiral and early-type galaxies (ETGs) taken from the Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel/ (KINGFISH) / Spitzer Infrared Nearby Galaxies Survey (SINGS) surveys. The photometric parameters of bulges are obtained from bulge-disc decompositions using Galfi data analysis algorithm. The method and corrections for projection and dust effects previously obtained are used to derive intrinsic photometric and structural bulge parameters. We show the main bulge scaling relations and the black hole relations, both observed and intrinsic ones, in B band. We find dust and inclination effects to produce more important changes in the parameters of the Kormendy relation for spiral galaxies, with the respective bulges of late-type galaxies (LTGs) residing on a steeper slope relation than the early-type galaxies (ETGs). We observe that the Kormendy relation in combination with a bulge Sérsic index (nb) threshold does not produce a conclusive morphological separation of bulges. The nb- bulge-to-total flux ratio (B/T) and B/T-stellar mass could be used to discriminate between LTGs and ETGs, while a further use of these parameters to divide bulges with different morphologies is problematic due to overlaps in the two distributions or large spread in values. We confirm the existence of two distinct intrinsic relations between the bulge luminosity (or absolute magnitude) and Sérsic index for LTGs and ETGs, while the relations between the black hole mass (MBH) and bulge luminosity are not found to be statistically different at p<0.05. Within errors, we find statistically similar intrinsic MBH − nb relations for all bulges.
Tesis sobre el tema "Spiral bulges"
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Proctor, Robert Neil. "Metallicities and stellar populations in spiral bulges". Thesis, University of Central Lancashire, 2002. http://clok.uclan.ac.uk/20825/.
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A major aim of current astrophysical research is the development of models of galaxy formation that are consistent with observational data. Until recently, the main tools of such research were broadband colours. However, the Lick system of indices has recently provided researchers with a more accurate tool for probing galaxy populations. The work in this thesis compares Lick indices in bright elliptical galaxies with those in the bulges of spiral galaxies, in an effort to compare, contrast and constrain their star formation histories. Long-slit spectroscopic observations of line-strengths and kinematics were carried out along the minor axes of 32 galaxies (ellipticals, SOs and spiral bulges). This study shows bulges to have central line-strengths comparable with those of single stellar populations of approximately solar metallicity or above. In bulges, central line-strengths are shown to lie close to, or within, the loci defining solar abundance ratio SSPs. The large number (24) of indices measured in this study, in conjunction with models of the effects of varying abundance ratios, permit the breaking of age/metallicity degeneracy and allow estimation of enhancements in specific light elements. Estimates of luminosity-weighted age, metallicity and abundance ratio show that, while early-type galaxies exhibit a large range of ages (2 to 13 Gyr), bulges are generally younger, and less enhanced in light elements. Trends involving age and metallicity also differ between early and late types. An anti-correlation is found between age and metallicity in early-type galaxies in the sample, while, in bulges, metallicity is correlated with velocity dispersion. Metallicity gradients are detected in all galaxies in the sample. Age gradients are also detected. No gradients are detected in abundance ratios. A "single zone with in-fall" model of galactic chemical evolution is used to constrain star formation histories of the galaxies observed. It is shown that monolithic collapse models can not reproduce the line-strengths observed in either early- or late-type galaxies. However, models including more extended star formation (e.g. mergers or secular evolution) can. The results of this work are, therefore, at odds with the received wisdom that bulges and elliptical galaxies are old and coeval, with indices in bulges more consistent with secular evolution models of formation, and those in early-type galaxies more consistent with merger models.
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Ballero, Silvia Kuna. "Evolution of chemical abundances in active and quiescent spiral bulges". Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2560.
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2006/2007In this thesis I develop a chemical evolution model which takes advantage of the most recent high-quality abundance observations in the Galactic bulge to put constraints on its formation and evolution and to obtain a baseline model for bulges in general. I adopt updated massive star nucleosynthesis and follow the evolution of several alpha-elements and Fe by varying the evolutionary parameters. The [alpha/Fe] ratios in the bulge are correctly predicted to be supersolar for a wide range in [Fe/H], and the stellar metallicity distribution is reproduced assuming a short formation timescale, a high star formation efficiency and an initial mass function flatter than the disk. Metallicity-dependent oxygen yields with stellar mass loss are included in the chemical evolution models for the bulge and the solar neighbourhood. The agreement between predicted and observed [O/Mg] trends above solar metallicity is significantly improved; a normalisation problem probably indicates that the adopted semi-empirical yields need adjustment. The difference between [O/Fe] and the other [alpha/Fe] ratios in the bulge and solar neighbourhood is explained. I test the so-called universal initial mass function, suitable for ellipticals and disks, to see if the bulge stellar metallicity distribution can be reproduced by varying the yields for very massive stars, and included M31 in my analysis. I show that assuming a flatter initial mass function than the universal one is necessary, and that a variation exists in the initial mass function among different environments. Finally, I investigate the evolution of spiral bulges hosting Seyfert nuclei, with detailed calculations of the galactic potential and of the feedback from the central supermassive black hole in an Eddington-limited accretion regime. New spectro-photometrical evolution codes covering a wide range of stellar ages and metallicities allowed to model the photometric features of local bulges. I successfully predict the observed black hole-host bulge mass relation. The observed present-day nuclear bolometric luminosity is achieved only for the most massive bulges, otherwise a rejuvenation is necessary. The observed high star formation rates and metallicities, constancy of chemical abundances with the redshift and bulge present-day colours are reproduced, but a steeper initial mass function is required to match the colour-magnitude relation and the present K-band bulge luminosity.
In questa tesi, ho sviluppato un modello di evoluzione chimica che si avvale di recenti osservazioni ad alta qualità di abbondanze chimiche nel bulbo della Via Lattea, per porre dei vincoli sui suoi meccanismi di formazione ed evoluzione e ottenere un modello generale per i bulbi di spirale. Ho adottato una nucleosintesi aggiornata per le stelle massicce e seguito l'evoluzione di diversi elementi-alpha e del ferro, variando i parametri evolutivi. Si prevede correttamente che i rapporti [alpha/Fe] nel bulbo siano soprasolari per un ampio intervallo in [Fe/H]. La distribuzione in metallicità è riprodotta con un tempo di formazione breve, un'alta efficienza di formazione stellare e una funzione iniziale di massa più piatta che nel disco. Yields di ossigeno con perdita di massa stellare in funzione della metallicità sono stati inclusi nei modelli di evoluzione chimica del bulbo e dei dintorni solari. L'accordo tra gli andamenti di [O/Mg] previsti e osservati per metallicità soprasolari risulta sensibilmente migliorato; si spiega inoltre la differenza tra il rapporto [O/Fe] e gli altri [alpha/Fe] nel bulbo e nei dintorni solari. Un problema di normalizzazione indica che probabilmente gli yields semi-empirici adottati necessitano una revisione. Ho verificato se con la cosiddetta funzione iniziale di massa universale, adeguata per galassie ellittiche e dischi, la distribuzione in metallicità stellare del bulge può essere riprodotta calibrando gli yields delle stelle supermassicce, includendo M31 nell'analisi. Si dimostra che una funzione iniziale di massa più piatta di quella universale è necessaria, e che esiste una variazione nella funzione iniziale di massa tra i diversi ambienti. Infine, ho studiato l'evoluzione di bulbi di spirali che ospitano galassie di Seyfert, mediante calcoli dettagliati del potenziale galattico e del feedback dal buco nero supermassiccio centrale in un regime di accrescimento limitato dal tasso di Eddington. Nuovi codici spettro-fotometrici che coprono un ampio intervallo di età stellari e di metallicità hanno permesso di modellizzare le caratteristiche fotometriche dei bulbi locali. La relazione osservata tra massa del buco nero e del bulbo ospite è prevista con successo. La luminosità bolometrica nucleare misurata al tempo presente si consegue solo per i bulbi più massicci, negli altri casi è necessario un "ringiovanimento". Le osservazioni di alto tasso di formazione stellare, alte metallicità, invarianza di abbondanze chimiche col redshift e colori dei bulbi locali sono riprodotte; una funzione iniziale di massa più ripida è invece richiesta per la relazione colore-magnitudo e la luminosità dei bulbi in banda K al tempo presente.
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Pastrav, Bogdan Adrian. "The effects of dust on the derived photometric parameters of disks and bulges in spiral galaxies". Thesis, University of Central Lancashire, 2013. http://clok.uclan.ac.uk/9604/.
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Spiral galaxies contain large amounts of interstellar dust, that absorbs and scatters their photons. This results in strong distortions and changes of their observed stellar images from what would be observed in the absence of the dust. Because of this the measured structural parameters of spiral galaxies, and indeed, knowledge of some of the most fundamental physical attributes of galaxies - their stellar distributions - is strongly biased. I present here the results of a study to quantify the effects of dust on the derived photometric parameters of disks (old stellar disks and young stellar disks) and bulges in spiral galaxies: scale-lengths, axis-ratios, central surface-brightness, effective radii and Sersic indices. The goal of this study is to provide corrections for dust effects to observers by following the procedures and algorithms they use to perform surface brightness photometry of real images of galaxies. The changes in the derived photometric parameters from their intrinsic values (as seen in the absence of dust) were obtained by fitting simulated images of disks and bulges produced using radiative transfer calculations. The fits to the simulations were performed using GALFIT 3.0.2 data analysis algorithm and the fitted models were the commonly used infinitely thin disks described by exponential, general Sersic and de Vaucouleurs distributions. The analysis was done firstly for disks and bulges seen in isolation (thus quantifying dust and projection effects) and subsequently for the same morphological components seen together (thus quantifying the dust effects on bulge-disk decomposition). This is the first time a systematic and self-consistent quantification of these effects has been performed covering the whole parameter space and all photometric parameters of spiral galaxies and its constituent stellar components. The approach proposed here allows a clear separation of projection effects, dust effects and decomposition effects, through chain corrections. For single morphological components, I find the young stellar disks to suffer the most severe variation in the photometric parameters due to dust effects. In this context I also present corrections for narrow line (Balmer line) images. Old stellar disks are also significantly affected by dust, in particular when fits are performed with exponential functions. The photometric parameters of bulges are to a lesser extent affected by dust. I also find that the variation of dust corrections with face-on dust opacity and inclination is similar for bulges with different intrinsic stellar emissivities (different Sersic index), with differences manifesting only close to edge-on orientations of the disk. Dust corrections for bulges are found to be insensitive to the choice of the truncation radius and ellipticity of the bulge. I find that dust effects on the photometric parameters of decomposed disks and bulges increase with the Sersic index of bulge intrinsic volume stellar emissivity distribution and depend on the bulge-to-disk ratio for galaxies with bulge stellar emissivity described by higher Sersic index functions. All the numerical results are listed in the Appendices and made available to the scientific community.
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Parmiggiani, Marco. "Environmental effects on the evolution of dwarf and spiral galaxies: dynamics and stellar populations". Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3427237.
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The work presented in this thesis is aimed at the observational characterization of the physical properties of galaxies to place constraints on their scenarios of formation and evolution. In particular, I have focused on the determination of how the environment in which galaxies evolve affects their structural and kinematic properties, and their stellar populations. In the first part of my thesis I studied the properties of the dwarf early-type galaxy population in two nearby galaxy clusters: Centaurus and Perseus. For the Centaurus Cluster, I analysed X-Shooter spectroscopy of a sample of eight dwarf elliptical galaxies and two compact elliptical galaxies. The visible arm high-resolution spectra were employed to derive the internal velocity dispersion of the galaxies, together with an estimate of their dynamical mass and their mass-to-light ratios. I used the internal velocity dispersion measurements to compute the first estimate of the Faber-Jackson relation of dwarf galaxies in the Centaurus Cluster. I used the medium resolution optical spectra to characterize the stellar populations of the dwarf and compact galaxies. In addition, I analysed fibre spectroscopic data of low-luminosity ellipticals in the Perseus Cluster. My investigation of the global cluster kinematics confirmed the different origin of the faint galaxy population with respect to the bright galaxies. Measurements of the properties of the stellar populations were performed on all the cluster early-type galaxies, and were used to derive the first estimate of the mass-metallicity relation for the Perseus Cluster. In the second part of my thesis I analysed the stellar populations of a sample of bulges in twelve isolated disc galaxies and in four spiral galaxies with a high surface brightness disc. I derived the structural parameters of the bulges by performing two-dimensional photometric decomposition of galaxy images. I analysed long-slit spectroscopy to derive the age, metallicity, and \afe\ enhancement in the central part of the bulge and at the radius where the bulge contributes the same surface brightness as the other galaxy components. The bulges of isolated galaxies are characterized by intermediate and old ages, a large spread in metallicities ranging from sub- to super-solar values, and super-solar [α/Fe] enhancements. The high [α/Fe] ratios indicates shorter star formation timescales with respect to galaxies in denser environments. All the sample bulges also show a negative gradient for the [α/Fe] enhancement, in agreement with the predictions of the dissipative collapse formation scenario. By comparing our analysis with those of selected samples from the literature, I was able to confirm that environment-driven processes play an important role in the evolution of bulges in high density environments. In particular, repeated interactions and merging with other galaxies tend to erase the stellar population gradients of the bulges and prolong their star formation histories.L'obiettivo del lavoro presentato in questa tesi è la caratterizzazione osservativa delle proprietà fisiche delle galassie, per vincolarne gli scenari di formazione ed evoluzione. In particolare mi sono concentrato nel determinare come l'ambiente, in cui evolvono le galassie, influisca sulle loro proprietà strutturali e cinematiche e sulle loro popolazioni stellari. La prima parte della tesi è focalizzata sulle proprietà delle galassie nane dei primi tipi morfologici negli ammassi di galassie del Centauro e di Perseo. Per l'Ammasso del Centauro, ho analizzato gli spettri ottenuti con X-Shooter di un campione di 8 galassie ellittiche nane e 2 galassie ellittiche compatte. Gli spettri nella banda ottica ad alta risoluzione sono stati utilizzati per ricavare la dispersione di velocità interna delle galassie, insieme alla stima della loro massa dinamica e del rapporto massa/luminosità. Ho utilizzato le dispersioni di velocità per calcolare la prima stima della relazione di Faber-Jackson per le galassie nane dell'Ammasso di Centaurus. Ho sfruttato gli spettri nella banda ultravioletta e blu a media risoluzione per caratterizzare le popolazioni stellari delle galassie nane e delle galassie compatte. Successivamente ho effettuato l'analisi di spettroscopia da fibre ottiche di galassie ellittiche a bassa luminosità nell'Ammasso di Perseuo. La mia indagine della cinematica globale dell'ammasso ha confermato la diversa origine della popolazione di galassie a bassa brillanza rispetto a quelle ad alta brillanza. La misura delle proprietà delle popolazioni stellari è stata condotta su tutte le galassie ellittiche e lenticolari dell'ammasso, ed ha permesso di ricavare la prima stima della relazione massa-metallicità per l'Ammasso di Perseo. Nella seconda parte della tesi ho analizzato le popolazioni stellari di un campione di sferoidi in 12 galassie a disco isolate ed in 4 galassie a spirale di alta brillanza superficiale. Ho derivato i parametri strutturali degli sferoidi attraverso la decomposizione fotometrica. Ho analizzato spettroscopia di fenditura per ricavare l'età, la metallicità, il rapporto [α/Fe] nella parte centrale degli sferoidi ed in corrispondenza del raggio dove lo sferoide contribuisce la stessa frazione di brillanza superficiale rispetto alle altre componenti della galassia. Gli sferoidi delle galassie isolate sono caratterizzati da età intermedie ed elevate, da una metallicità molto varia e da alti valori di del rapporto [α/Fe], che indicano come i tempi scala di formazione stellare siano più corti rispetto a quelli delle galassie in ambienti più densi. Tutti gli sferoidi del campione presentano anche gradienti del rapporto [α/Fe] negativi, in accordo con le previsioni del modello di formazione per collasso dissipativo. Confrontando la mia analisi con campioni selezionati dalla letteratura, ho potuto confermare che i processi di interazione con l'ambiente hanno un ruolo importante nell'evoluzione degli sferoidi in ambienti ad alta densità. In particolare, interazioni ripetute e fusioni con altre galassie tendono a cancellare i gradienti nelle popolazioni stellari degli sferoidi e prolungano i tempi di formazione stellare.
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Sauvaget, Tabatha. "Formation des pseudo-bulbes dans les galaxies spirales locales de masse intermédiaire via des fusions majeures riches en gaz". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEO012/document.
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Les bulbes sont présents dans environ 80% des galaxies spirales locales de masse intermédiaire. Les galaxies spirales représentent environ 70% des galaxies de masse intermédiaire (typiquement avec des masses comprises entre 2 × 10^10 et 10^11 masses solaires) de l’Univers local. Alors que les bulbes classiques sont généralement associés aux résultats de fusions, les pseudo-bulbes sont plutôt associés à l’évolution séculaire. Cependant, le modèle cosmologique ΛCDM prévoit une croissance hiérarchique des galaxies par les fusions alors que l’on trouve plus de 50% de pseudo-bulbes dans les galaxies spirales de masse intermédiaire de l’Univers local. Le but de la thèse est de vérifier s’il est possible de construire des pseudo-bulbes à partir de fusions majeures riches en gaz. La première partie de cette thèse est consacrée à la présentation du sujet ainsi qu’à l’état de l’art sur la formation et l’évolution des bulbes galactiques.La deuxième partie de cette thèse porte sur la description de la méthodologie mise en place pour analyser les bulbes des galaxies spirales et comprendre leur formation. La thèse com- porte deux axes d’études, une partie observationnelle avec l’analyse de deux échantillons complets de galaxies spirales locales de masse intermédiaire pour déterminer la proportion de pseudo-bulbes dans ces échantillons et avoir une référence robuste. Une autre partie, qui est le coeur de l’étude, est dédiée à l’analyse de simulations numériques de fusions majeures de deux progéniteurs riches en gaz réalisées avec un code N-body/Hydrodynamique (GADGET2). L’objectif est de reproduire ce type de galaxies et d’étudier leurs propriétés grâce à une décomposition bulbe+disque.Dans la troisième partie, je montre que, dans les limites données par les simulations, nous pou- vons reproduire des galaxies spirales présentant des pseudo-bulbes via des fusions majeures riches en gaz. Cette thèse propose un nouveau scénario de formation des pseudo-bulbes grâce à la formation de barres durant les fusions majeures qui permet d’amener du gaz dans les parties centrales. De plus, beaucoup de structures observées comme des barres, anneaux ou double-disques sont reproduits dans les simulations. Les différents paramètres des simulations ont ensuite été modifiés (fraction de gaz, rapport de masses, masse des progéniteurs, feedback, extension du gaz, pericentre) pour explorer leur impact sur les résultats. On constate que les disparités des indices de Sersic et des rapports B/T proviennent autant de la différence entre les orbites que de celle entre les paramètres physiques initiaux choisis pour les simulations, mais certaines grandes tendances peuvent tout de même être extraites. Par exemple, l’étude montre que plus la fraction de gaz des progéniteurs est élevée, plus les indices Sersic et le rapport B/T diminuent, plus le nombre de barres et leur taille augmententBulges are present in almost 80% of nearby spiral galaxies of intermediate mass. Spiral galaxies represent about 70% of the intermediate-mass galaxies (typically with a mass between 2 × 10^10 and 10^11 solar masses) in the local Universe. While classical bulges have been associated to the result of major mergers, pseudo-bulges have been rather associated to secular evolution. However, the cosmological ΛCDM model predicts a hierarchical growth of galaxies via mergers while pseudo-bulges are found in > 50% of large nearby spiral galaxies. The aim of this thesis is to verify if we can build pseudo-bulges with gas-rich major mergers. The first part of this thesis is devoted to the presentation of the subject and the state of the art on the formation and evolution of galactic bulges.The second part of this thesis is focusing on the methodology developped to analyse bulges of spiral galaxies and understand their formation. The thesis has two axes of study, an observational part with the analysis of two complete samples of local spiral galaxies of intermediate mass to determine the proportion of pseudo-bulges in these samples and to have a reliable reference. Another part, which is the core of the study, is dedicated to the analysis of nume- rical simulations of gas-rich major mergers done with a N-body / SPH code (GADGET2). The aim is to reproduce this type of galaxy and to study their properties thanks to a bulge + disk decomposition.In the third part, I show that, within the limits given by the simulations, we can reproduce spiral galaxies with pseudo-bulges via gas-rich major mergers. This thesis propose a new scenario of pseudo-bulge formation thanks to the formation of a bar, which bring gas into the central parts. In addition, most of the observed structures, such as bars, rings or double-disks, are reproduced in the simulations. The different parameters of simulations has been then modified (gas fraction, mass ratio, mass of progenitors, feedback, gas extension, pericenter) to explore their impact on the results. We found that the disparities on Sersic index and B/T ratio comes as much from the difference between orbits as from between initial physical parameters chosen for simulations but we can still extract some trends. For instance, I show that the higher the gas fraction of the progenitors, the lower the Sersic index and the B/T ratio, the more the number of bars and their size increases
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Maubon, Grégory. "Rôle de la barre dans l'évolution des galaxies spirales". Lyon 1, 2001. http://www.theses.fr/2001LYO10249.
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Depuis quelques années, l'importance de la barre dans l'évolution des galaxies spirales n'est plus remise en cause. Cette importance apparaît à la fois dans les observations et dans les simulations. Cette thèse est une contribution à l'étude de l'influence de la barre sur l'évolution des galaxies spirales. Elle se décompose en trois parties : 1. J'ai d'abord extrait les indices spectrophotométriques centraux Mg2 et
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Clain-Chamosset-Yvrard, Lise. "Prix d'actifs, bulles et fluctuations macroéconomiques". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM2018.
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Cette thèse traite des interactions entre les sphères financière et réelle de l'économie. Elle se compose de quatre chapitres. Dans les deux premiers chapitres, nous étudions l'existence et les fluctuations d'une bulle spéculative rationnelle, comme source de la volatilité des prix d'actifs, en prenant en compte les imperfections financières dans la modélisation des choix des ménages. L'existence d'un choix de portefeuille et de frictions financières favorisent l'émergence des fluctuations d'une bulle et des cycles économiques endogènes. Dans un tel contexte, nous analysons le rôle stabilisateur des politiques fiscales et/ou monétaires. Dans le chapitre 1, nous montrons qu'une politique monétaire répondant aux prix des actifs permet de stabiliser l'économie dans son ensemble. Dans le chapitre 2, nous comparons les vertus stabilisatrices d'un impôt progressif sur le revenu de capital à celles d'une politique monétaire régie par une règle de Taylor. Nous montrons qu'un impôt progressif sur le capital permet de stabiliser l'économie en réduisant la probabilité d'apparition des fluctuations endogènes, alors qu'une règle de Taylor a des vertus stabilisatrices mitigées. Nous étudions, dans le chapitre 3, l'existence de bulles rationnelles dans une économie ouverte à deux pays et la transmission internationale de leur éclatement. L'éclatement de la bulle dans un pays se transmet nécessairement à l'autre pays. L'effet de l'éclatement peut être positif ou négatif sur l'autre pays. Dans le chapitre 4, nous analysons le rôle de l'hétérogénéité sur la dynamique des prix d'actifs et les inégalités lorsque les agents ont des préférences pour la richesseThis thesis deals with the interplay between the financial and real sectors of the economy. This thesis consists of four chapters. In the first two chapters, we study the existence and endogenous fluctuations of rational speculative bubbles, as a source of volatility in asset prices, taking into account the financial imperfections at the household level. We argue that the existence of a portfolio choice and financial frictions promote the emergence of bubble fluctuations and endogenous business cycles. In this context, we analyze the stabilizing role of fiscal and/or monetary policies. In Chapter 1, we show that a monetary policy responding to asset prices can stabilize the economy as a whole. In Chapter 2, we compare the stabilizing virtues of a progressive taxation on capital income with those of a monetary policy managed by a Taylor rule. We show that a progressive taxation on capital may rule out endogenous fluctuations, whereas a monetary policy under a Taylor rule has a mitigated stabilizing role. In Chapter 3, we study, the existence of rational bubbles in a two-country economy, and the international transmission of their bursting. A bubble bursting in a country necessarily transmits to the othercountry. The effect of a bubble crash in one country onthe bubble issued by the other country can be positive or negative. In Chapter 4, we analyze the role of heterogeneity on the dynamics of asset prices and inequalities when economic agents have preferences for wealth. Heterogeneity in preferences, but also in income, can heighten social inequalities and increase the asset price in the long run, but also promote asset price volatility in the short run
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Van, Ruymbeke Bruno. "Etude expérimentale des régimes de coexistence toroïdal/spiral en écoulement de Taylor Couette diphasique avec injection de bulles Quantitative visualization of swirl and cloud bubbles in Taylor–Couette flow, in Journal of Visualization 20, 2017". Thesis, Brest, 2018. http://www.theses.fr/2018BRES0059.
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Notre étude, expérimentale, s’inscrit dans le contexte de la réduction de frottement de paroi par injection de bulles millimétriques. Elle fait suite aux travaux de Mehel (2006), et de Fokoua (2013). On s’intéresse à la modulation du frottement, aux caractéristiques des cellules de Taylor et à la structuration de la phase gazeuse, pour des régimes de coexistence (alternance de motifs toroïdal-spiral). La géométrie d’entrefer est caractérisée par un rapport des rayons de 0,9. Le Reynolds varie entre [1700-50000] et la fraction volumétrique d’air entre [0-0,1%]. Par visualisations haute fréquence et analyse des défauts (dislocations et fusions de cellules), on a caractérisé la transition entre les régimes de coexistence structurée, coexistence déstructurée et chaos développé. Par Stéréo-PIV (2D3C), on a caractérisé la phase liquide dans un plan méridien et discriminé les contributions respectives des mouvements aléatoire et cohérent à la turbulence. Les mesures en simultané du couple exercé sur le cylindre intérieur ont mis en évidence que différents mécanismes influencent le frottement de paroi : cisaillement turbulent dû au sillage des bulles, dû aux jets entre cellules et relaxation du gradient de vitesse azimutale. L’analyse en fonction des motifs et des régimes montre que le couple maximum est atteint pour le motif toroïdal en régime structuré. Les images haute fréquence des bulles ont été analysées en discriminant les bulles par leur position radiale dans l’entrefer. On obtient des lois de similitude pour le taux de vide et la vitesse axiale du gaz en fonction des nombres de Froude de rotation des cellules ou du cylindre intérieur. La fraction volumétrique d’air contrôle la vitesse ascensionnelle des cellules, la vitesse azimutale du gaz et la fréquence de l’onde azimutaleThis experimental study deals with wall friction reduction by injection of millimetric bubbles. This work is in the continuity of Mehel (2006) and Fokoua (2013) PHDs. We focus on the friction modulation, Taylor's cells characteristics and the gas phase structure, for coexistence regimes (alternance between toroidal-spiral patterns). The gap geometry is characterized by the ratio of radii (0,9). The Reynolds and the air volumetric fraction are varied in the ranges [1700-50000] and [0-0,1%] respectively. By high-frequency visualizations and defect (dislocations and cell fusions) analysis method, we characterized the transition between the regimes of structured coexistence, unstructured coexistence and developed chaos. By Stereo-PIV (2D3C) measurements, we characterized the liquid phase in a meridian plane and discriminated the contributions of random and coherent motions to the turbulence. Simultaneous measurements of the torque exerted on the inner cylinder evidence different mechanisms influencing the wall friction: turbulent shear either due to the bubbles wake or to the jets between cells and relaxation of the azimuthal velocity gradient. The analysis according to the patterns and regimes shows that the maximum torque is reached for the toroidal pattern and structured regime. The high frequency images of the bubbles were analyzed by discriminating their radial position in the gap. Self-similar laws with respect to the rotational Froude numbers either characterizing the cells or the inner cylinder are obtained for both void fraction and axial velocity of the gas phase. The air volumetric fraction controls the rising velocity of the cells, the azimuthal velocity of the gas and the frequency of the azimuthal wave
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Bastié-Chassagne, Sandrine. "Paralysie bulbo-spinale familiale : à propos de deux cas". Bordeaux 2, 1998. http://www.theses.fr/1998BOR2M036.
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Williams, Michael J. "Early-type disk galaxies". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:936168ab-f49a-410a-9e1b-80c7ad7cf556.
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In this thesis I investigate the dynamics and stellar populations of a sample of 28 edge-on early-type (S0--Sb) disk galaxies, 22 of which host a boxy or peanut-shaped bulge. I begin by constructing mass models of the galaxies based on their observed photometry and stellar kinematics. Subject to cosmologically motivated assumptions about the shape of dark haloes, I measure in a purely dynamical way their stellar and dark masses. I make a preliminary comparison between the dynamically determined stellar masses and those predicted by stellar population models. I then compare the Tully-Fisher (luminosity--velocity) relations of the spirals and S0s in the sample. I show that S0s are systematically fainter at a given rotational velocity, but the amount by which they are fainter is less than expected by models in which they are the products of truncation of star formation in spirals. This raises the possibility that S0s are smaller or more concentrated than spirals of the same mass. I then study the vertical structure of the boxy and peanut-shaped bulges of a subset of the sample. Among this sample of five galaxies, I find one example in which the stellar populations show no evidence that the bulge and the disk formed in different processes, and in which the bulge is in perfectly cylindrical rotation, i.e. its line-of-sight velocity does not change with height above the disk. This galaxy is probably a pure disk galaxy. However, even with this small sample, I also show that cylindrical rotation and homogeneous stellar populations are not ubiquitous properties of boxy and peanut-shaped bulges. Finally I analyse central and radial trends in the stellar populations of the bulges of full sample of 28 galaxies. I find that, at a given velocity dispersion, the central stellar populations of these barred early-type disk galaxies are identical to those of elliptical galaxies, which suggests that secular evolution does not dominate the centre of these galaxies. However, the radial metallicity gradients are shallower than those of ellipticals. This is qualitatively consistent with chemodynamical models of bar formation, in which radial inflow and outflow smears out pre-existing gradients.
Libros sobre el tema "Spiral bulges"
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Sandler, Corey. Official Sega Genesis and Game Gear strategies, 3RD Edition. New York: Bantam Books, 1992.
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Tom, Badgett, ed. Official Sega Genesis and Game Gear strategies, 2ND Edition. Toronto: Bantam Books, 1991.
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Official Sega Genesis and Game Gear Strategies, '94 Edition. New York, NY: Random House, Electronic Publishing, 1993.
Buscar texto completoCapítulos de libros sobre el tema "Spiral bulges"
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Zaritsky, Dennis, Marcia Rieke y Hans-Walter Rix. "IR Imaging of Spiral Galaxy Bulges". En Galactic Bulges, 441–42. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-0922-2_91.
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Renzini, Alvio. "Origin of Bulges". En Spiral Galaxies in the Near-IR, 95–104. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-540-49739-4_12.
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Gerhard, O. E. y M. Vietri. "Triaxial Bulges in Spiral Galaxies". En Dynamics and Interactions of Galaxies, 342–43. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-75273-5_81.
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Jablonka, Pascale. "Stellar Populations in Bulges of Spiral Galaxies". En Galaxy Scaling Relations: Origins, Evolution and Applications, 140–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-540-69654-4_17.
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Jablonka, Pascale, Javier Gorgas y Paul Goudfrooij. "Stellar Populations in Bulges of Spiral Galaxies". En The Evolution of Galaxies, 367–70. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-017-3311-3_82.
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Peletier, Reynier y Marc Balcells. "Stellar Populations of Bulges and Disks: New Insights from Near-IR Colours". En Spiral Galaxies in the Near-IR, 48–57. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-540-49739-4_7.
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Ferguson, Henry C., Arthur F. Davidsen y Gerard A. Kriss. "The Hot Stellar Component in Elliptical Galaxies and Spiral Bulges". En The Stellar Populations of Galaxies, 291–95. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2434-8_39.
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Graham, Alister W. y Mercedes Prieto. "On the Light-Profiles of Spiral Galaxy Bulges and the Hubble Sequence for Spirals". En Toward a New Millennium in Galaxy Morphology, 653–54. Dordrecht: Springer Netherlands, 2000. http://dx.doi.org/10.1007/978-94-011-4114-7_71.
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Jablonka, P., N. Arimoto y P. Martin. "The Overabundance of Magnesium Over Iron in Bulges of Spiral Galaxies". En New Light on Galaxy Evolution, 395. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0229-9_107.
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Gorgas, J., P. Jablonka y P. Goudfrooij. "Line-Strength Gradients and Stellar Populations in the Bulges of Spiral Galaxies". En Highlights of Spanish Astrophysics III, 99–102. Dordrecht: Springer Netherlands, 2003. http://dx.doi.org/10.1007/978-94-017-1778-6_22.
Texto completoActas de conferencias sobre el tema "Spiral bulges"
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Botirov, F. U. y S. N. Nuritdinov. "Nonlinear cosmogony of the spiral galaxy bulges". En ASTRONOMY AT THE EPOCH OF MULTIMESSENGER STUDIES. Proceedings of the VAK-2021 conference, Aug 23–28, 2021. Crossref, 2022. http://dx.doi.org/10.51194/vak2021.2022.1.1.142.
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An early idea of one of the authors of this work is being developed, where the mechanism of instability of the warpperturbation mode against the background of an non-stationary disk was proposed for the first time in [1]. For this purpose,a model of a nonlinearly non-stationary self-gravitating disk with an anisotropic velocity diagram was first constructed. Themodel has a composite nature, or rather, it is a superposition of isotropic and anisotropic states of the disk. A nonstationaryanalogue of the dispersion equation of this composite model in the general case is obtained. The behavior of the domeddisturbance mode, the instability of which leads to the formation of a classical bulge in the central region of the disk, isinvestigated. Critical diagrams of the dependence of the virial ratio on the degree of rotation of the system for various valuesof the superposition parameter and the corresponding diagrams for the increments of instability are constructed.
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Fabricius, Maximilian H., Stuart Barnes, Ralf Bender, Niv Drory, Frank Grupp, Gary J. Hill, Ulrich Hopp y Phillip J. MacQueen. "VIRUS-W: an integral field unit spectrograph dedicated to the study of spiral galaxy bulges". En SPIE Astronomical Telescopes + Instrumentation, editado por Ian S. McLean y Mark M. Casali. SPIE, 2008. http://dx.doi.org/10.1117/12.787204.
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Fabricius, Maximilian H., Frank Grupp, Ralf Bender, Niv Drory, Jim Arns, Stuart Barnes, Claus Gössl et al. "VIRUS-W: commissioning and first-year results of a new integral field unit spectrograph dedicated to the study of spiral galaxy bulges". En SPIE Astronomical Telescopes + Instrumentation, editado por Ian S. McLean, Suzanne K. Ramsay y Hideki Takami. SPIE, 2012. http://dx.doi.org/10.1117/12.925177.
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Lu, Hong, Xiangang Su, Xinbao Zhang, Yongquan Zhang, Wei Fan y Shaojun Wang. "An Effective Spiral Trajectory Generation Approach for the Turning of Piston Skirt With Middle-Bulged Varying Ellipse". En ASME 2017 12th International Manufacturing Science and Engineering Conference collocated with the JSME/ASME 2017 6th International Conference on Materials and Processing. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/msec2017-2702.
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Given the chord length of equal angle isn’t equal on elliptical section of piston skirt with middle-bulged varying ellipse (PSMVE), a larger theoretical processing error will inevitably be introduced with the interpolation algorithm of equal angle for PSMVE. To improve the manufacturing precision of PSMVE, a novel interpolation algorithm of equal-length-chord and spiral-line (IAES) and a method of tool radius compensation are presented based on symbolic computation. Firstly, a three-dimensional model of PSMVE is generated through the symbolic computation method, meanwhile, the coordinate values of arbitrary cutter-contact point can be expressed accurately. Secondly, the turning spiral trajectory is generated via updated cutter-contact point which can be searched from the obtained cutter-contact point with equal length chord. Besides, this paper proposes a method of tool radius compensation and obtains the cutter location points through appropriate transformation of coordinates. Last, some simulation, which mainly includes the establishment of 3D model, the generation of spiral trajectory with equal-length-chord, the transformation between cutter-contact point and cutter-location points, is carried out. In addition, this paper takes CNC turning center (System: SINUMERIK 802C) as an example to complete the processing of PSMVE. Experiment results verify that the machining method is appropriate for PSMVE.
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Thorbole, Chandrashekhar K., M. Jorgensen y H. M. Lankarani. "Assessment of the Dynamic Response of a Lumbar Spine Functional Unit Under Axial Compressive High Loading Rate: Outcome on the Axial Disc Bulge and its Relation to the Load Magnitude". En ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66019.
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Human lumbar spine tolerance to the compressive impact loading is less when compared to its tolerance to the perpendicular dynamic load. The dynamic response of the functional spinal unit in compressive loading is governed by the viscoelastic behavior of the IVD (Intervertebral disc). The axial bulge of the disc is the result of viscoelastic nature of the nucleus which tends to swell under high loading rate. This characteristic causes the end-plate to bow into the cancellous bone as it is supported by the strong cortical bone on its periphery. The end-plate is one of the important elements in the functional spinal unit if failed results disc material to progress into the vertebral body beneath it. This paper quantifies the axial bulge of the end-plate under dynamic compressive load using Finite Element Method. A simple validated axis symmetry FE model is employed to identify the most vulnerable lumbar spine level using the sensitivity analysis. This is followed by the development of more detailed FE model with viscoelastic modeling of the nucleus and the annulus. The dynamic load is applied on the superior vertebral body which follows triangular loading profile with 50ms rise time. The axial bulge is quantified at the center of the disc as this is the location of maximum deflection and local stress in the end-plate. The ratio of axial bulge and the total FSU deflection is plotted against magnitude of load applied to gain insight regarding the relation between load magnitude and axial bulge. This study will complement the research on end-plate fracture mechanism and its role in causing the burst fracture based on the magnitude of load.
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Bahramshahi, N., H. Ghaemi y K. Behdinan. "Finite Element Study of Spinal Cord Mechanics During Biomechanical Response of Middle Cervical Spine". En ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40573.
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The present study is conducted to develop a detailed FE model of spinal cord and to study its behaviour under various loading conditions. To achieve the goal, a previously developed and validated FE model of the middle cervical spine (C3-C5) is utilized. The model is further modified to investigate the stresses that the spinal cord in experiences during cervical spine motion segment in compression and flexion/extension loading modes. The resulting Von Misses stress and axial strain of the anterior and posterior surfaces of the cervical spinal cord are obtained from a set of elements along the C4-C5 disc space of the dural sheath, CSF and cord. The results show that in compression, the anterior surface of spinal cord experiences larger displacement, stress, and strain than those of the posterior surface. Conversely, the analyses show that in flexion\extension, the stresses, strains, and displacements are more pronounced in posterior segment of the spinal cord. In extension, the posterior disc bulge applies pressure onto the Posterior Longitudinal Ligament and thereby, applying local pressure on the spinal cord. The FE results show a stress concentration at the point of contact between disc and spinal cord. Furthermore, the FE results of flexion test show similar stress concentration characteristic at the point of contact. However, the local stress on spinal cord is more pronounced in flexion than extension at the C4-C5 area of spinal cord. It was also determined the compressive load resulted in the highest stress concentration on the spinal cord.
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Bahramshahi, N., H. Ghaemi y K. Behdinan. "Development and Validation of a Three-Dimensional Finite Element Model of Cervical Spine (C3-C5)". En ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-40567.
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The objective of this investigation is to develop a detailed, non-linear asymmetric three-dimensional anatomically and mechanically accurate FE model of complete middle cervical spine (C3-C5) using Hypermesh and MSC.Marc software. To achieve this goal, the components of the cervical spine are modeled using 20-noded hexagonal elements. The model includes the intervertebral disc, cortical bone, cancellous bone, endplates, and ligaments. The structure and dimensions of each spinal component are compared with experimentally measured values. In addition, the soil mechanics formulation of MSC.Marc finite element software is applied to model the mechanical behaviour of vertebrae and intervertebral discs as linear isotropic two-phase (biphasic) material. The FE simulation is conducted to investigate compression, flexion\extension and right\Left lateral bending modes. The simulation results are validated and compared closely with the published experimental data and the existing FE models. In general, results show greater flexibility in flexion and less flexibility in extension. The flexion/extension curves are asymmetric with a greater magnitude in flexion than in extension. In addition, the variations of the predicted lateral C4-C5 disc bulge are investigated and the results show that the maximum disc bulge occurs at the C4-C5 anterior location.
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Raheem, Hassan M., Willie “Skip” E. Rochefort y Brian K. Bay. "Digital Image Correlation Method in Measuring the Out of Plane Displacement: A Case Study on an Artificial Intervertebral Disc". En ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23305.
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Abstract We have developed a simple, low-cost, and innovative design — known as a “disc emulator” to mimic the mechanical response of a motion segment (vertebra - intervertebral disc-vertebra) of the human spinal column under axial compression loads. The disc emulator consists of upper and lower components that mimic the human vertebrae and a middle component that represents the annulus fibrosus (AF). This study aims to investigate the effects of changing the stiffness of artificial annulus fibrosus of the disc emulator on the bulging measurements while performing compression tests on the disc emulator. A non-contact measurement — digital image correlation (DIC) — was used for the bulging measurements. The results show that the bulging at the posterior region for the discs without nucleus pulposus (NP) bulged inwards, but the bulging at the posterolateral region was outwards, which accords with the reported behavior of the human disc, for the disc without and with NP regardless of the stiffness of the discs. Changing the stiffness of the artificial annulus fibrosus (AAF) alters the bulging magnitudes in the disc, which shows similar responses with respect to the available data on the human disc. The emulator provides a convenient experimental platform for evaluating normal and pathological disc states and assessing the biomechanics of potential therapeutic interventions.
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Feng, Qingshan, Yi-han Lin, Bin Li y Hanchen Song. "Failure Assessment for Girth Weld Defects of Pipeline". En 2010 8th International Pipeline Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ipc2010-31211.
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This paper studies some key issues of fitness-for-service assessment for pipelines constructed in 1970s in Northeastern China, which were found to have large amount of weld defects resulting in leakage and rupture accidents. The mechanical behaviors of tensile strength, Charpy V-notch impact energy and fracture toughness are tested for the spiral weld metal and pipeline steel, showing that the state standards of steel for pressure vessel are still met after serving for more than 30 years. The safety limit line of the failure assessment diagram (FAD) is derived according to BS7910: level 2B assessment, based on the obtained stress-strain curve of weld metal. The chemical composition of pipeline steel analyzed by the energy spectrum method indicates the pipeline was made of 16Mn steel. The metallographic examination reveals that the metallurgical structure of weld metal was composed of ferrite and pearlite with five different zones. The morphology of tensile fractured surface shown by ductile dimples indicates the tensile fracture is of ductile type, which implies the weld metal and pipeline steel after long time service have not yet become brittle. The stress magnification factor for the bulge effect of through-wall girth defect is extracted from the stress intensity factor evaluated by the finite element simulation method, indicating the applicable ranges of Kastner solution and Schulze et al solution. The stress magnification factor caused by the bending stress of the misalignment imperfection of girth weld joint is calculated by FEM to review the applicability of relevant formulas given in BS7910 for engineering critical assessment. Finally, it is concluded by FE simulation that though the stress magnification effect of shallow cracks in weld toe zone is significant, it may be insignificant in its fracture failure assessments.
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Albeanu, Grigore, Henrik Madsen y Florin Popentiuvladicescu. "LEARNING FROM NATURE: NATURE-INSPIRED ALGORITHMS". En eLSE 2016. Carol I National Defence University Publishing House, 2016. http://dx.doi.org/10.12753/2066-026x-16-158.
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During last decade, the nature has inspired researchers to develop new algorithms [1, 2, 3]. The largest collection of nature-inspired algorithms is biology-inspired: swarm intelligence (particle swarm optimization, ant colony optimization, cuckoo search, bees algorithm, bat algorithm, firefly algorithm etc.), genetic and evolutionary strategies, artificial immune systems etc. As well-known examples, the following have to be mentioned: aircraft wing design, wind turbine design, bionic car, bullet train, optimal decisions related to traffic, appropriate strategies to survive under a well-adapted immune system etc. Based on collective social behavior of organisms, researchers had developed optimization strategies taking into account not only the individuals, but also groups and environment [1]. However, learning from nature, new classes of approaches can be identified, tested and compared against already available algorithms. After a short introduction, this work review the most effective, according to their performance, nature-inspired algorithms, in the second section. The third section is dedicated to learning strategies based on nature oriented thinking. Examples and the benefits obtained from applying nature-inspired strategies in problem solving are given in the fourth section. Concluding remarks are given in the final section. References 1. G. Albeanu, B. Burtschy, Fl. Popentiu-Vladicescu, Soft Computing Strategies in Multiobjective Optimization, Ann. Spiru Haret Univ., Mat-Inf Ser., 2013, 2, http://anale-mi.spiruharet.ro/upload/full_2013_2_a4.pdf 2. H. Madsen, G. Albeanu, and Fl. Popentiu-Vladicescu, BIO Inspired Algorithms in Reliability, In H. Pham (ed.) Proceedings of the 20th ISSAT International Conference on Reliability and Quality in Design, Reliability and Quality in Design, August 7-9, 2014, Seattle, WA, U.S.A. 3. N. Shadbolt, Nature-Inspired Computing, http://www.agent.ai/doc/upload/200402/shad04_1.pdf