bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of reionization on dwarf galaxy formation
Authors: Ricotti Massimo 
Published: December 2008

AbstractIn this talk I revisit the problem of gas accretion onto minihalos after reionization. I show that primordial minihalos with vcir < 20 km s−1 stop accreting gas after reionization, as is usually assumed, but in virtue of their increasing concentration and the decreasing temperature of the intergalactic medium as redshift decreases, they have a late phase (at redshift z<2) of gas accretion and possibly star formation. As a result we expect that pre-reionization fossils have a more complex star formation history than previously envisioned. A signature of this model is a bimodal star formation history. The dwarf spheroidal galaxy Leo T, that inspired the present work, fits with this scenario. Another prediction of the model is the existence of a population of gas rich minihalos that never formed stars. A subset of compact high-velocity clouds may be identified as such objects but the bulk of them may still be undiscovered.
Young Star Clusters in the Small Magellanic Cloud: Impact of Local and Global Conditions on Star Formation
Authors: Sabbi Elena , Smith Linda J. , Carlson Lynn R. , Nota Antonella , Tosi Monca , Cignoni Michele , Gallagher Jay S. , Sirianni Marco , Meixner Margaret 
Published: December 2008

AbstractWe compared deep images acquired with the Advanced Camera for Surveys on board of the Hubble Space Telescope with mid-IR Spitzer Space Telescope images and University College London Echelle Spectrograph spectra of NGC 346 and NGC 602, two of the youngest star clusters in the Small Magellanic Cloud. Our multi-wavelength approach allowed us to infer very different origins for the clusters: while NGC 346 is likely the result of the hierarchical collapse of a giant molecular cloud, NGC 602 is probably the result of the collision and consequent interaction of two H I shells of gas.
Dwarf galaxies and the Magnetisation of the IGM
Authors: Klein Uli 
Published: December 2008

AbstractWith the operation of LOFAR, a great opportunity exists to shed light on a problem of some cosmological significance. Diffuse radio synchrotron emission not associated to any obvious discrete sources as well as Faraday rotation in clusters of galaxies both indicate that the intergalactic or intracluster medium (IGM, ICM) is pervaded by a weak magnetic field, along with a population of relativistic particles. Both, particles and fields must have been injected into the IGM either by Active Galactic Nuclei (AGN) or by normal star-forming galaxies. Excellent candidates for the latter are starburst dwarf galaxies, which in the framework of hierarchical structure formation must have been around in large numbers. If this is true, one should be able to detect extended synchrotron halos of formerly highly relativistic particles around local starburst or post-starburst dwarf galaxies. With LOFAR, one should easily find these out to the Coma Cluster and beyond.
First Stars – Type Ib Supernovae Connection
Authors: Nomoto Ken'ichi , Tanaka Masaomi , Kamiya Yasuomi , Tominaga Nozomu , Maeda Keiichi 
Published: December 2008

AbstractThe very peculiar abundance patterns observed in extremely metal-poor (EMP) stars can not be explained by conventional normal supernova nucleosynthesis but can be well-reproduced by nucleosynthesis in hyper-energetic and hyper-aspherical explosions, i.e., Hypernovae (HNe). Previously, such HNe have been observed only as Type Ic supernovae. Here, we examine the properties of recent Type Ib supernovae (SNe Ib). In particular, SN Ib 2008D associated with the luminous X-ray transient 080109 is found to be a more energetic explosion than normal core-collapse supernovae. We estimate that the progenitor's main sequence mass isMMS= 20 − 25M⊙with an explosion of kinetic energy ofEK~ 6.0 × 1051erg. These properties are intermediate between those of normal SNe and hypernovae associated with gamma-ray bursts. Therefore, such energetic SNe Ib could also make an important contribution to the chemical enrichment in the early Universe.
Powerful explosions atZ= 0?
Authors: Ekström Sylvia , Meynet Georges , Hirschi Raphael , Maeder André 
Published: December 2008

AbstractMetal-free stars are assumed to evolve at constant mass because of the very low stellar winds. This leads to large CO-core mass at the end of the evolution, so primordial stars with an initial mass between 25 and 85M⊙are expected to end as direct black holes, the explosion energy being too weak to remove the full envelope.We show that when rotation enters into play, some mass is lost because the stars are prone to reach the critical velocity during the main sequence evolution. Contrary to what happens in the case of very low- but non zero-metallicity stars, the enrichment of the envelope by rotational mixing is very small and the total mass lost remains modest. The compactness of the primordial stars lead to a very inefficient transport of the angular momentum inside the star, so the profile of Ω(r) is close to Ωr2= const. As the core contracts, the rotation rate increases, and the star ends its life with a fast spinning core. Such a configuration has been shown to modify substantially the dynamics of the explosion. Where one expected a weak explosion or none at all, rotation might boost the explosion energy and drive a robust supernova. This will have important consequences in the way primordial stars enriched the early Universe.
Wind anisotropy and stellar evolution
Authors: Georgy Cyril , Meynet Georges , Maeder André 
Published: December 2008

AbstractMass loss is a determinant factor which strongly affects the evolution and the fate of massive stars. At low metallicity, stars are supposed to rotate faster than at the solar one. This favors the existence of stars near the critical velocity. In this rotation regime, the deformation of the stellar surface becomes important, and wind anisotropy develops. Polar winds are expected to be dominant for fast rotating hot stars.These polar winds allow the star to lose large quantities of mass and still retain a high angular momentum, and they modify the evolution of the surface velocity and the final angular momentum retained in the star's core. We show here how these winds affect the final stages of massive stars, according to our knowledge about Gamma Ray Bursts. Computation of theoretical Gamma Ray Bursts rate indicates that our models have too fast rotating cores, and that we need to include an additional effect to spin them down. Magnetic fields in stars act in this direction, and we show how they modify the evolution of massive star up to the final stages.
Low-Mass and Metal-Poor Gamma-Ray Burst Host Galaxies
Authors: Savaglio Sandra 
Published: December 2008

AbstractGamma-ray bursts (GRBs) are cosmologically distributed, very energetic and very transient sources detected in the γ-ray domain. The identification of their x-ray and optical afterglows allowed so far the redshift measurement of 150 events, from z = 0.01 to z = 6.29. For about half of them, we have some knowledge of the properties of the parent galaxy. At high redshift (z > 2), absorption lines in the afterglow spectra give information on the cold interstellar medium in the host. At low redshift (z < 1.0) multi-band optical-NIR photometry and integrated spectroscopy reveal the GRB host general properties. A redshift evolution of metallicity is not noticeable in the whole sample. The typical value is a few times lower than solar. The mean host stellar mass is similar to that of the Large Magellanic Cloud, but the mean star formation rate is five times higher. GRBs are discovered with γ-ray, not optical or NIR, instruments. Their hosts do not suffer from the same selection biases of typical galaxy surveys. Therefore, they might represent a fair sample of the most common galaxies that existed in the past history of the universe, and can be used to better understand galaxy formation and evolution.
The Luminosity Function of Long Gamma-Ray Burst and their rate at z ≥ 6
Authors: Salvaterra R. , Campana S. , Chincarini G. , Choudhury T. R. , Covino S. , Ferrara A. , Gallerani S. , Guidorzi C. , Tagliaferri G. 
Published: December 2008

AbstractWe compute the luminosity function (LF) and the formation rate of long gamma ray bursts (GRBs) in three different scenarios: i) GRBs follow the cosmic star formation and their LF is constant in time; ii) GRBs follow the cosmic star formation but the LF varies with redshift; iii) GRBs form preferentially in low–metallicity environments. We then test model predictions against the Swift 3-year data, showing that scenario i) is robustly ruled out. Moreover, we show that the number of bright GRBs detected by Swift suggests that GRBs should have experienced some sort of luminosity evolution with redshift, being more luminous in the past. Finally we propose to use the observations of the afterglow spectrum of GRBs at z ≥ 5.5 to constrain the reionization history, and then applied our method to the case of GRB 050904.
Dust properties and distribution in dwarf galaxies
Authors: Lisenfeld Ute , Relaño Monica , Vílchez José , Battaner Eduardo , Hermelo Israel 
Published: December 2008

AbstractWe present a study of the extinction, traced by the Balmer decrement, in HII regions in the dwarf galaxies NGC 1569 and NGC 4214. We find that the large-scale extinction around the most prominent HII regions in both galaxies forms a shell in which locally the intrinsic extinction can adopt relatively high values (AV= 0.8 − 0.9 mag) despite the low metallicity and thus the low overall dust content. The small-scale extinction (spatial resolution ~0.3″) shows fluctuations that are most likely due to variations in the dust distribution. We compare the distribution of the extinction to that of the dust emission, traced bySpitzeremission at 8 and 24μm, and to the emission of cold dust at 850μm. We find in general a good agreement between all tracers, except for the 850μm emission in NGC 4214 which is more extended than the extinction and the other emissions. Whereas in NGC 1569 the dust emission at all wavelengths is very similar, NGC 4214 shows spatial variations in the 24-to-850μm ratio.We furthermore compared the 24μm and the extinction-corrected Hα emission from HII regions in a sample of galaxies with a wide range of metallicities and found a good correlation, independent of metallicity. We suggest that this lack of dependence on metallicity might be due to the formation of dust shells with a relatively constant opacity, like the ones observed here, around ionizing stars.
Stars at Low Metallicity in Dwarf Galaxies
Authors: Tolstoy Eline , Battaglia Giuseppina , Cole Andrew 
Published: December 2008

AbstractDwarf galaxies offer an opportunity to understand the properties of low metallicity star formation both today and at the earliest times at the epoch of the formation of the first stars. Here we concentrate on two galaxies in the Local Group: the dwarf irregular galaxy Leo A, which has been the recent target of deep HST/ACS imaging (Cole et al. 2007) and the Sculptor dwarf spheroidal, which has been the target of significant wide field spectroscopy with VLT/FLAMES (Battaglia 2007).
The size-density relation of H ii regions in blue compact dwarf galaxies
Authors: Hirashita Hiroyuki , Hunt Leslie K. 
Published: December 2008

AbstractWe investigate the size-density relation of H ii regions in blue compact dwarf galaxies (BCDs) by compiling observational data of their size (Di) and electron density (ne). We find that the size-density relation follows a relation with constant column density (ne ∝ Di−1) rather than with constant luminosity (ne ∝ Di−1.5). Such behavior resembles that of Galactic H ii regions, and may imply an underlying “scale-free” connection. Because this size-density relation cannot be explained by static models, we model and examine the evolution of the size-density relation of H ii regions by considering the star formation history and pressure-driven expansion of H ii regions. We find that the size-density relation of the entire BCD sample does not result from an evolutionary sequence of H ii regions but rather reflects a sequence with different initial gas densities (or “hierarchy” of density). We also find that the dust extinction of ionizing photons is significant for the BCD sample, despite their blue optical colors. This means that as long as the emission from H ii regions is used to trace massive star formation, we would miss the star formation activity in dense environments even in low-metallicity galaxies such as BCDs.
Ionized gas in dwarf galaxies: Abundance indicators
Authors: Stasińska Grażyna 
Published: December 2008

AbstractWe discuss the four basic methods to derive HII region abundances in metal-poor galaxies by presenting a few recent results obtained with these methods. We end up by commenting on the yet unsolved problem of temperature fluctuations in HII regions, which may plague abundance determinations, as well as the discrepancy between abundances derived from recombination lines and collisionally excited lines, to which inhomogeneous chemical composition might be the explanation.
SMC in space and time: a project to study the evolution of the prototype interacting late-type dwarf galaxy
Authors: Tosi M. , Gallagher J. , Sabbi E. , Glatt K. , Grebel E. K. , Christian C. , Cignoni M. , Clementini G. , Cole A. , Da Costa G. , Harbeck D. , Marconi M. , Meixner M. , Nota A. , Sirianni M. , Smecker-Hane T. 
Published: December 2008

AbstractWe introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we present the Colour-Magnitude Diagrams (CMDs) resulting from HST/ACS photometry, aimed at deriving the star formation history (SFH) in six fields of the SMC. The fields are located in the central regions, in the stellar halo, and in the wing toward the LMC. The CMDs are very deep, well beyond the oldest Main Sequence Turn-Off, and will allow us to derive the SFH over the entire Hubble time.
A New Age and Distance for I Zw 18, the Most Metal-Poor Galaxy in the Nearby Universe
Authors: Aloisi A. , Clementini G. , Tosi M. , Annibali F. , Contreras R. , Fiorentino G. , Mack J. , Marconi M. , Musella I. , Saha A. , Sirianni M. , van der Marel R. P. 
Published: December 2008

AbstractThe blue compact dwarf galaxy I Zw 18 holds the record of the lowest metallicity ever observed in the local universe. As such, it represents the closest analog to primordial galaxies in the early universe. More interestingly, it has recurrently been regarded as a genuinely young galaxy caught in the process of forming in the nearby universe. However, stars of increasingly older ages are found within I Zw 18 every time deeper high-resolution photometric observations are performed with the Hubble Space Telescope (HST): from the original few tens of Myrs to, possibly, several Gyrs. Here we summarize the history of I Zw 18 age and present an ongoing HST/ACS project which allowed us to precisely derive the galaxy distance by studying its Cepheid variables, and to firmly establish the age of its faintest resolved populations.
Psychiatric and Behavioral Genetics: A Useful Distinction?
Authors: Hallmayer Joachim 
Published: December 2008

AbstractDr. Hallmayer began with a discussion of the Nuffield Council on Bioethics' work on genetics, mental disorders and human behavior. He further explored psychiatric genetics and urged against the oversimplification of dynamic interactions. To watch Dr. Hallmayer’s presentation, please see the "Google Video posting.":http://video.google.com/videoplay?docid=-5387564337084407366&hl=enTo watch the deliberative discussion concluding the first Symposium panel, please see the "Google Video posting.":http://video.google.com/videoplay?docid=3871777823134971240&hl=en
Psychiatric Genetics: Methods, Findings and Ethical Issues
Authors: Kendler Kenneth 
Published: December 2008

AbstractThis talk has 4 major sections. First, I review the basic definition of a complex trait, especially as it applies to psychiatric disorders. Second, I outline the 4 basic paradigms of psychiatric genetics: simple genetic epidemiology, advanced genetic epidemiology, gene-finding methods and molecular genetics. Third, I review a few basic facts about psychiatric genetics - the level of heritabilities found for most common disorders and the difficulties the field has had in obtaining replicated evidence for single gene effects. Finally, I briefly review three conceptual/philosophical issues that relate to psychiatric genetics: i) why do people become much more concerned in learning about possible genetic influences on personality or risk for depression than genes that influence risk for cancer, atherosclerosis or asthma? ii) how have the results of research in behavioral/Psychiatric Genetics impacted on the sense of Parental Responsibility for psychiatric illness in their offspring.To watch Dr. Kendler’s presentation, please see the "Google Video posting.":http://video.google.com/videoplay?docid=-3261606556062804269&hl=en
Determination of adsorptive and diffusive properties of carbon dioxide - methane - water in coal-like structures using molecular simulations
Authors: Salih Alaaeldin , Müller Erich 
Published: December 2008

AbstractThis work employs molecular modeling to simulate both the equilibrium and kinetic behavior pertaining adsorption/desorption and permeation of carbon dioxide within the enhanced coal bed methane (ECBM) process and the corresponding CO~2~ sequestration processes in deep coal mines. The coal structure is modeled on the basis of a carbon, nanotubes, slit pores and more realistic “virtual” carbons. (from bottom up in the figure) The grand canonical Monte Carlo method is used to simulate the adsorption isotherms and isosteric heats of adsorption of the methane-carbon dioxide-water ternary mixture into the carbon structure, while Molecular Dynamics is applied to the same systems to study the competitive diffusion properties of these fluids and to observe the preferential pathways associated with the non-equilibrium flow (kinetics) within these nanoporous media. Although this study focuses on using a rigid carbon matrix, approaches to introducing dynamic carbon structures that mimic the swelling behaviour of coals are discussed.
An Integrated IGCC-CSS Design Course for Graduate Students in Petroleum Engineering
Authors: Falcone Gioia , Jafarpour Behnam , Barrufet Maria 
Published: December 2008

AbstractA new graduate course on CO2 Capture and Uses was offered for the first time at Texas A&M, Pet. Eng., in Fall 2008. A multidisciplinary team of instructors from the Pet. Eng. & Chem. Eng. departments was assembled to ensure the appropriate expertise.The objective of the course is to let the students understand the need for / potential of Carbon Capture and Storage (CCS) & Enhanced Oil Recovery (EOR).
Design of carbon dioxide storage
Authors: Blunt Martin 
Published: December 2008

AbstractCarbon capture and storage (CCS) – the collection of carbon dioxide (CO~2~) from industrial sources and its injection underground – is an important technology to reduce CO~2~ emissions to the atmosphere, mitigating climate change. The North Sea, with mature hydrocarbon fields and saline aquifers offers an attractive storage location for CO~2~ produced by the UK’s gas and coal-fired power plants. The principal concern with CCS is to ensure that the CO~2~ does not leak into the oceans or atmosphere over hundreds or thousands of years. We propose a storage strategy where CO~2~ and brine are injected together followed by brine injection alone. We predict that using this technique around 95% of the CO~2~ can be rendered immobile in pore-scale (10s micron) droplets in the porous rock. Over thousands to billions of years the CO~2~ may dissolve or precipitate as carbonate, but it will not migrate upwards and so is effectively sequestered. This design is demonstrated through numerical simulation of field-scale flow through a North Sea aquifer coupled to an experimentally-based model of small-scale trapping. The CO~2~ is trapped during the decades-long lifetime of the injection phase, avoiding the need for extensive monitoring for centuries. The method does not rely on impermeable cap rock to contain the CO~2~; this is only a secondary containment for the small amount of remaining mobile gas. Furthermore, the reduced mobility ratio between injected and displaced fluids leads to a more uniform sweep of the aquifer leading a larger storage capacity than injecting CO~2~ alone.
Reactivation of Limestone-Derived Sorbents using Hydration: Preliminary Results From a Fluidised Bed
Authors: Blamey John , Fennell Paul , Dugwell Denis 
Published: December 2008

AbstractA simple method of CO~2~ capture is by using the calcium looping cycle. The calcium looping cycle uses CaCO~3~ as a CO~2~ carrier, via the reversible reaction CaO(s) + CO~2~(g) = CaCO~3~(s), to extract CO2 from the exhaust stream and provide a pure stream of CO~2~ suitable for sequestration. A problem associated with the technology is that the capacity of the sorbent to absorb CO~2~ reduces significantly with the number of cycles of carbonation and calcination. The energy penalty of the cycle is considerably increased by cycling unreacted sorbent: hydration of unreactive sorbent has emerged as a promising strategy of reducing this penalty by regenerating the reactivity of exhausted sorbent.A small atmospheric pressure fluidised bed reactor has been built and tested, that allows repeated cycling between two temperatures up to 1000 °C. Work presented here focuses on the effects of variation of the calcination temperature before hydration. Hydration has been found to more than double the reactivity of a spent sorbent cycled under the mildest conditions studied (calcination temperature of 840 °C). However, as calcination temperature is increased the observed reactivation decreases until little reactivation is observed for the sorbent cycled at 950 °C. The primary reason for this appears to be a substantial increase in friability of particles, with reactivity normalised for mass losses appearing similar independent of cycling temperature.
Improving the worthiness of the Elder problem as a benchmark for buoyancy driven convection models
Authors: van Reeuwijk Maarten , Mathias Simon , Simmons Craig , Ward James 
Published: December 2008

AbstractAn important trapping mechanism associated with the geosequestration of CO~2~ is that of dissolution into the formation water. Although supercritical CO~2~ is significantly less dense than water, experimental data reported in the literature show that the density of an aqueous solution of CO~2~ could be slightly greater. Under normal situations, the transfer of gas to solution is largely controlled by the relatively slow process of molecular diffusion. However, the presence of variable densities can trigger off gravity instabilities leading to much larger-scale convection processes. Such processes can potentially enhance rates of dissolution by an order of magnitude. Consequently there is a need for future performance assessment models to incorporate buoyancy driven convection (BDC). A major issue associated with BDC models is that of grid convergence when benchmarking to the Elder problem. The Elder problem originates from a heat convection experiment whereby a rectangular Hele-Shaw cell was heated over the central half of its base. A quarter of the way through the experiment, Elder (1967) observed six plumes, with four narrow plumes in the center and two larger plumes at the edges. As the experiment progressed, only four plumes remained. The issue is that depending on the grid resolution used when seeking to model this problem, modelers have found that different schemes yield steady states with either one, two or three plumes. The aim of this paper is to clarify and circumvent the issue of multiple steady state solutions in the Elder problem using a pseudospectral method.