bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chemically tagging the Galactic disk: abundance patterns of old open clusters
Authors: De Silva G. M. , Freeman K. C. , Bland-Hawthorn J. 
Published: March 2009

AbstractThe long term goal of large-scale chemical tagging is to use stellar elemental abundances as a tracer of dispersed substructures of the Galactic disk. The identification of such lost stellar aggregates and exploring their chemical properties will be key in understanding the formation and evolution of the disk. Present day stellar structures such as open clusters and moving groups are the ideal testing grounds for the viability of chemical tagging, as they are believed to be the remnants of the original larger star-forming aggregates. We examine recent high resolution abundance studies of open clusters to explore the various abundance trends and reassess the prospects of large-scale chemical tagging.
Bars in Cuspy Dark Halos
Authors: Dubinski John , Berentzen Ingo , Shlosman Isaac 
Published: March 2009

AbstractWe examine the bar instability in models with an exponential disk and a cuspy NFW-like dark matter (DM) halo inspired by cosmological simulations. Bar evolution is studied as a function of numerical resolution in a sequence of models spanning 104 – 108 DM particles - including a multi-mass model with an effective resolution of 1010. The goal is to find convergence in dynamical behaviour. We characterize the bar growth, the buckling instability, pattern speed decay through resonant transfer of angular momentum, and possible destruction of the DM halo cusp. Overall, most characteristics converge in behaviour for halos containing more than 107 particles in detail. Notably, the formation of the bar does not destroy the density cusp in this case. These higher resolution simulations clearly illustrate the importance of discrete resonances in transporting angular momentum from the bar to the halo.
Kinematical & Chemical Characteristics of the Thin and Thick Disks
Authors: Wyse Rosemary F. G. 
Published: March 2009

AbstractI discuss how the chemical abundance distributions, kinematics and age distributions of stars in the thin and thick disks of the Galaxy can be used to decipher the merger history of the Milky Way, a typical large galaxy. The observational evidence points to a rather quiescent past merging history, unusual in the context of the ‘consensus’ cold-dark-matter cosmology favoured from observations of structure on scales larger than individual galaxies.
The chemical fingerprints of the thin and the thick disk
Authors: Feltzing Sofia , Oey Sally , Bensby Thomas 
Published: March 2009

AbstractThe past history and origin of the different Galactic stellar populations are manifested in their different chemical abundance patterns. We obtained new elemental abundances for 553 F and G dwarf stars, to more accurately quantify these patterns for the thin and thick disks. However, the exact definition of disk membership is not straightforward. Stars that have a high likelihood of belonging to the thin disk show different abundance patterns from those for the thick disk. In contrast, we show that stars for the Hercules Stream do not show unique abundance patterns, but rather follow those of the thin and thick disks. This strongly suggests that the Hercules Stream is a feature induced by internal dynamics within the Galaxy rather than the remnant of an accreted satellite.
Beryllium and the formation of the Thick Disk and of the Halo
Authors: Pasquini Luca , Smiljanic R. , Bonifacio P. , Gratton R. , Galli D. , Randich S. 
Published: March 2009

AbstractWe use Beryllium to investigate star formation in the early Galaxy. Be has been demonstrated to be a good indicator of time in these early epochs. By analyzing the so-far largest sample of halo and thick disk metal poor stars, we find a clear scatter in Be for a given value of [Fe/H] and [O/H]. The scatter is very pronounced for Halo stars, while it is marginal for thick disk stars. Our halo stars separate in the [α/Fe] - Be diagram, showing two main branches: one indistinguishable from the thick disk stars, and one with lower [α/Fe] ratio. The stars belonging to this branch are characterized by highly eccentric orbits and small perigalactic radius (Rmin). Their kinematics are consistent with an accreted component.
The initial luminosity and mass functions of Galactic open clusters
Authors: Zinnecker Hans , Piskunov Anatoly E. , Kharchenko Nina V. , Röser Siegfried , Schilbach Elena , Scholz Ralf-Dieter 
Published: March 2009

AbstractWe have derived a complete magnitude-limited sample of 440 Galactic open clusters in the solar neighborhood, with integrated V-magnitude brighter than 8 mag. This sample can be used to infer the present-day luminosity and mass functions of open clusters up to a given age; it can even be used to construct the initial mass and luminosity function (IMF, ILF) of clusters (defined as visible clusters with age 4 – 8 Myr). The high-mass end of the cluster IMF is a power-law with a slope of −2 or slightly shallower (−1.7) while the luminous cluster ILF has a power-slope of −1, in agreement with what is found for extragalactic clusters. Both distribution functions show a turnover, starting at 300 M⊙ and integrated magnitude −3 mag, respectively. The overall birthrate of clusters is 0.4 clusters per kpc2 and per Myr. The average present-day cluster mass is 700 M⊙, while the average initial cluster mass is 4500 M⊙. The difference of these two average masses indicates the high infant mortality and/or weight loss of Galactic open clusters (due to dynamical evolution).
Star Formation in Disks: Spiral Arms, Turbulence, and Triggering Mechanisms
Authors: Elmegreen Bruce G. 
Published: March 2009

AbstractStar formation is enhanced in spiral arms because of a combination of orbit crowding, cloud collisions, and gravitational instabilities. The characteristic mass for the instability is 107M⊙in gas and 105M⊙in stars, and the morphology is the familiar beads on a string with 1-2 kpc separation. Similar instabilities occur in resonance rings and tidal tails. Sequential triggering from stellar pressure occurs in two ways. For short times and near distances, it occurs in the bright rims and dense knots that lag behind during cloud dispersal. For long times, it occurs in swept-up shells and along the periphery of cleared regions. The first case should be common but difficult to disentangle from independent star formation in the same cloud. The second case has a causality condition and a collapse condition and is often easy to recognize. Turbulent triggering produces a hierarchy of dense cloudy structure and an associated hierarchy of young star positions. There should also be a correlation between the duration of star formation and the size of the region that is analogous to the size-linewidth relation in the gas. The cosmological context is provided by observations of star formation in high redshift galaxies. Sequential and turbulent triggering is not yet observable, but gravitational instabilities are, and they show a scale up from local instabilities by a factor of ~3 in size and ~100 in mass. This is most easily explained as the result of an increase in the ISM turbulent speed by a factor of ~5. In the clumpiest galaxies at high redshift, the clumps are so large that they should interact with each other and merge in the center, where they form or contribute to the bulge.
Evolution and chemical and dynamical effects of high-mass stars
Authors: Meynet Georges , Chiappini Cristina , Georgy Cyril , Pignatari Marco , Hirschi Raphael , Ekström Sylvia , Maeder André 
Published: March 2009

AbstractWe review general characteristics of massive stars, present the main observable constraints that stellar models should reproduce. We discuss the impact of massive star nucleosynthesis on the early phases of the chemical evolution of the Milky Way (MW). We show that rotating models can account for the important primary nitrogen production needed at low metallicity. Interestingly such rotating models can also better account for other features as the variation with the metallicity of the C/O ratio. Damped Lyman Alpha (DLA) systems present similar characteristics as the halo of the MW for what concern the N/O and C/O ratios. Although in DLAs, the star formation history might be quite different from that of the halo, in these systems also, rotating stars (both massive and intermediate) probably play an important role for explaining these features. The production of primary nitrogen is accompanied by an overproduction of other elements as13C,22Ne and s-process elements. We show also how the observed variation with the metallicity of the number ratio of type Ibc to type II supernovae may be a consequence of the metallicity dependence of the line-driven stellar winds.
Chemical Yields from Supernovae and Hypernovae
Authors: Nomoto Ken'ichi , Wanajo Shinya , Kamiya Yasuomi , Tominaga Nozomu , Umeda Hideyuki 
Published: March 2009

AbstractWe review the final stages of stellar evolution, supernova properties, and chemical yields as a function of the progenitor's mass. (1) 8 - 10M⊙stars are super-AGB stars when the O+Ne+Mg core collapses due to electron capture. These AGB-supernovae may constitute an SN 2008S-like sub-class of Type IIn supernovae. These stars produce little α-elements and Fe-peak elements, but are important sources of Zn and light p-nuclei. (2) 10 - 90M⊙stars undergo Fe-core collapse. Nucleosynthesis in aspherical explosions is important, as it can well reproduce the abundance patterns observed in extremely metal-poor stars. (3) 90 - 140M⊙stars undergo pulsational nuclear instabilities at various nuclear burning stages, including O and Si-burning. (4) Very massive stars withM≳ 140M⊙either become pair-instability SNe, or undergo core-collapse to form intermediate mass black holes if the mass loss is small enough.
Effects of Supernova Feedback on the Formation of Galaxies
Authors: Scannapieco Cecilia , Tissera Patricia B. , White Simon D. M. , Springel Volker 
Published: March 2009

AbstractWe study the effects of Supernova (SN) feedback on the formation of galaxies using hydrodynamical simulations in a ΛCDM cosmology. We use an extended version of the code GADGET-2 which includes chemical enrichment and energy feedback by Type II and Type Ia SN, metal-dependent cooling and a multiphase model for the gas component. We focus on the effects of SN feedback on the star formation process, galaxy morphology, evolution of the specific angular momentum and chemical properties. We find that SN feedback plays a fundamental role in galaxy evolution, producing a self-regulated cycle for star formation, preventing the early consumption of gas and allowing disks to form at late times. The SN feedback model is able to reproduce the expected dependence on virial mass, with less massive systems being more strongly affected.
Chemodynamical simulations of the Milky Way Galaxy
Authors: Kobayashi Chiaki 
Published: March 2009

AbstractWe simulate the chemodynamical evolution of the Milky Way Galaxy, including the nucleosynthesis yields of hypernovae and a new progenitor model for Type Ia Supernovae (SNe Ia). In our nucleosynthesis yields of core-collapse supernovae, we use light curve and spectral fitting to individual supernovae to estimate the mass of the progenitor, the explosion energy, and the iron mass produced. A large contribution of hypernovae is required from the observed abundance of Zn ([Zn/Fe] ~0). In our progenitor model of SNe Ia, based on the single degenerate scenario, the SN Ia lifetime distribution spans a range of 0.1–20 Gyr with peaks at both ~ 0.1 and 1 Gyr. A metallicity effect from white dwarf winds is required from the observed trends of elemental abundance ratios (i.e., [(α,Mn,Zn)/Fe]-[Fe/H] relations). In our simulated Milky Way-type galaxy, the kinematical and chemical properties of the bulge, disk, and halo are broadly consistent with observations. 80% of the thick disk stars are older than ~8 Gyr and tend to have larger [α/Fe] than in the thin disk.
Chemical evolution of the Galaxy disk in connection with large-scale winds
Authors: Tsujimoto Takuji , Bland-Hawthorn Joss , Freeman Kenneth C. 
Published: March 2009

AbstractComparison of elemental abundance features between old and young thin disk stars may reveal the action of ravaging winds from the Galactic bulge, which once enriched the whole disk, and set up the steep abundance gradient in the inner disk (RGC ≲ 10–;12 kpc) and simultaneously the metallicity floor ([Fe/H]~ −0.5) in the outer disk. After the end of a crucial influence by winds, chemical enrichment through accretion of a metal-poor material from the halo onto the disk gradually reduced the metallicity of the inner region, whereas an increase in the metallicity proceeded beyond a solar circle. This results in a flattening of abundance gradient in the inner disk, and our chemical evolution models confirm this mechanism for a flattening, which is in good agreement with the observations. Our scenario also naturally explains an observed break in the metallicity floor of the outer disk by young stars since the limit of self-enrichment in the outer disk is supposed to be [Fe/H]≲ −1 and inevitably incurs a direct influence of the dilution by a low-metal infall whose metallicity is [Fe/H]~ −1. Accordingly, we propose that the enrichment by large-scale winds is a crucial factor for chemical evolution of the disk, and claim to reconsider the models thus far for the disk including the solar neighborhood, in which the metallicity is predicted to monotonously increase with time. Furthermore, we anticipate that a flattening of abundance gradient together with a metal-rich floor in the outer disk are the hallmark of disk galaxies with significant central bulges.
Cold Dark Matter Substructure and Galactic Disks
Authors: Kazantzidis Stelios , Zentner Andrew R. , Bullock James S. 
Published: March 2009

AbstractWe perform a set of high-resolution, fully self-consistent dissipationless N-body simulations to investigate the influence of cold dark matter (CDM) substructure on the dynamical evolution of thin galactic disks. Our method combines cosmological simulations of galaxy-sized CDM halos to derive the properties of substructure populations and controlled numerical experiments of consecutive subhalo impacts onto initially-thin, fully-formed disk galaxies. We demonstrate that close encounters between massive subhalos and galactic disks since z ~ 1 should be common occurrences in ΛCDM models. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. One typical host halo merger history is used to seed controlled N-body experiments of subhalo-disk encounters. As a result of these accretion events, the disk thickens considerably at all radii with the disk scale height increasing in excess of a factor of 2 in the solar neighborhood. We show that interactions with the subhalo population produce a wealth of distinctive morphological signatures in the disk stars, many of which resemble those being discovered in the Milky Way (MW), M31, and in other disk galaxies, including: conspicuous flares; bars; low-lived, ring-like features in the outskirts; and low-density, filamentary structures above the disk plane. These findings highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution.
Hydrodynamical Adaptive Mesh Refinement Simulations of Disk Galaxies
Authors: Gibson Brad K. , Courty Stéphanie , Sánchez-Blázquez Patricia , Teyssier Romain , House Elisa L. , Brook Chris B. , Kawata Daisuke 
Published: March 2009

AbstractTo date, fully cosmological hydrodynamic disk simulations to redshift zero have only been undertaken with particle-based codes, such as GADGET, Gasoline, or GCD+. In light of the (supposed) limitations of traditional implementations of smoothed particle hydrodynamics (SPH), or at the very least, their respective idiosyncrasies, it is important to explore complementary approaches to the SPH paradigm to galaxy formation. We present the first high-resolution cosmological disk simulations to redshift zero using an adaptive mesh refinement (AMR)-based hydrodynamical code, in this case, RAMSES. We analyse the temporal and spatial evolution of the simulated stellar disks' vertical heating, velocity ellipsoids, stellar populations, vertical and radial abundance gradients (gas and stars), assembly/infall histories, warps/lopsideness, disk edges/truncations (gas and stars), ISM physics implementations, and compare and contrast these properties with our sample of cosmological SPH disks, generated with GCD+. These preliminary results are the first in our long-term Galactic Archaeology Simulation program.
Plasma carotenoids, retinol and tocopherol levels and the risk of ovarian cancer
Authors: JEONG NAN‐HEE , SONG EUN‐SEOP , LEE JONG‐MIN , LEE KWANG‐BEOM , KIM MI‐KYUNG , CHEON JI‐EUN , LEE JAE‐KWAN , SON SUNG‐KYONG , LEE JUNG‐PIL , KIM JAE‐HOON , HUR SOO‐YOUNG , KWON YONG‐IL 
Published: March 2009

AbstractObjective. We investigated the relation between plasma carotenoids, retinol and tocopherol levels and ovarian cancer risk in Korean women. Design. Hospital‐based case–control study. Setting. Six tertiary medical institutes in Korea. Population. Forty‐five epithelial ovarian cancers and 135 age‐matched controls. Methods. Preoperative plasma concentrations of β‐carotene, lycopene, zeaxanthin plus lutein, retinol, α‐tocopherol, and γ‐tocopherol were measured by reverse‐phase, gradient high‐pressure liquid chromatography. Main outcome measures. Odds ratios (OR) and 95% confidence intervals (95%CI) were estimated by tertiles to evaluate the effect of micronutrients on endometrial cancer risk after adjustment for body mass (BMI) index, menopause, parity, oral contraceptive use, smoking status, and alcohol consumption status. Results. Women in the highest tertile for β‐carotene had 0.12‐times the risk of ovarian cancer of in the lowest tertile (OR 0.12; 95%CI 0.04–0.36). Women with the highest tertiles of lycopene (OR 0.09; 95%CI 0.03–0.32), zeaxanthin/lutein (OR 0.21; 95%CI 0.09–0.52), retinol (OR 0.45; 95%CI 0.21–0.98), α‐tocopherol (OR 0.23; 95%CI 0.10–0.53) and γ‐tocopherol (OR 0.28; 95%CI 0.11–0.70) had lower risk of ovarian cancer than women in the lowest tertiles. Results were consistent across strata of socio‐epidemiologic factors. Conclusions. Micronutrients, specifically ß‐carotene, lycopene, zeaxanthin, lutein, retinol, α‐tocopherol, and γ‐tocopherol, may play a role in reducing the risk of ovarian cancer.
Evaluation of Postnatal Weight Growth in Very Low Birth Weight Infants
Authors: Bertino Enrico , Milani Silvano , Boni Luisa , Coscia Alessandra , Rossetti Gessica , Testa Tiziana , Giuliani Francesca , Appino Irene , Spada Elena , Fabris Claudio 
Published: March 2009

ABSTRACTThere is general agreement about the need for longitudinal studies of very low birth weight infants (VLBWI) to evaluate their postnatal growth and to generate distance and velocity charts that allow neonatologists and pediatricians to detect earlier whether a child is not growing adequately. There are no satisfactory growth charts for VLBWI. We analyzed the weight growth of 262 VLBWIs from birth to 2 years of corrected age. Individual growth profiles were fitted with a 7‐constant exponential‐logistic function suitable for modelling weight growth pattern. After a postnatal weight loss, all VLBWIs showed a late neonatal peak of velocity between the seventh and 21st weeks; the large majority of them also experienced an early neonatal peak between the second and the sixth weeks. Small‐for‐gestational‐age VLBWIs with major morbidities grew less than reference appropriate‐for‐gestational‐age VLBWIs without major morbidities: at 2 years, the difference in weight was about 860 g. The more severe growth impairment in VLBWIs with major morbidities was almost entirely due to the reduced height of the late neonatal peak of velocity. The mathematical function used in this study is expected to be a useful tool to trace model‐based longitudinal distance and velocity charts specific for VLBWIs. Moreover, this function also could be used to evaluate to what extent different pathological conditions or nutritional and medical care protocols affect growth kinetics.
Probiotics in Preterm Infants: A Controversial Issue
Authors: Isolauri Erika 
Published: March 2009

ABSTRACTCurrent research is directed toward innovative dietary compositions that exert specific effects on health promotion and reducing the risk of diseases. For example, the demonstration that the gut microbiota is an important constituent in the intestine's mucosal barrier has led to new therapeutic strategies for infections as well as allergic and inflammatory conditions. Specific probiotic bacteria have been shown to stabilize the gut microbial environment and the intestine's permeability barrier, and to enhance systemic and mucosal IgA responses. These comprise important targets in the preterm infant, who is particularly susceptible to infection and inflammation and in whom the immature enterocyte responds to intraluminal antigens with proinflammatory cytokines. Recent data point to differences in immunomodulatory effects between candidate probiotic bacteria. Each probiotic strain is a unique component itself, and each strain has specific properties that cannot be extrapolated from other, even closely related, strains. Therefore, these properties of probiotic bacteria should be characterized during preclinical and clinical evaluations. Furthermore, because probiotics are a tool with which to modify the gut barrier and microbiota, the strains used must be obtained from acceptable sources with a proven safety record and efficacy to guarantee their future clinical applications. The approach of supplementation with single components, however, overlooks the role of dietary composition, with its range of nutrients and other potentially active components, and also the conceivable combined effects. Consequently, research now focuses both on characterizing specific probiotic strains and on how the food matrix and the dietary content interact with the most efficient probiotic strains.
Nutrition of Preterm Infants After Hospital Discharge
Authors: Griffin Ian J , Cooke Richard J 
Published: March 2009

ABSTRACTGrowth failure in preterm infants remains extremely common despite advances in neonatal care. Many, or even a majority, leave the hospital with weights below the 10th centile for age. Because of this, the possibility of nutritional interventions to improve postdischarge growth has been considered. A variety of interventions have been tested in randomized controlled trials in formula‐fed infants. Although the studies vary in design and in the intervention used, on balance the evidence supports the use of fortified formulas in formula‐fed preterm infants after hospital discharge. Specially designed postdischarge formulas and preterm infant formulas seem equally efficacious. The situation for infants fed human milk is much less clear. Although the postdischarge growth in human milk–fed infants is not as good as in formula‐fed infants, no interventions have been examined in human milk–fed infants in a randomized study, to our knowledge. We are unaware of any evidence that any of the commonly proposed nutritional interventions in human milk–fed infants after hospital discharge are either safe or efficacious. In the absence of such evidence, it seems prudent to avoid untested interventions in this population and to concentrate our efforts on the encouragement of breast‐feeding after hospital discharge.