bluuebunny/crossref_metadata_2025 huggingface dataset:
A Neglectful Parenting Style Moderates the Effect of the Verbal Threat Information Pathway on Children's Heart Rate Responses to Novel Animals
Authors: Price-Evans Khanya , Field Andy P.
Published: June 2008

Parenting styles are associated with anxiety in children. Part of this association can be explained by how parenting interacts with known pathways to anxiety. Although parenting interacts with the verbal threat information pathway to create anxiogenic cognitions in children, it is not known whether parenting styles mediate the physiological component of the anxiety emotion. An experiment is reported in which 6–10-year-old children (N = 54) completed parenting styles, and anxiety beliefs questionnaires. They were then given threat, positive or no verbal information about three novel animals before being asked to place their hands in boxes they believed these animals inhabited. Their average heart rate during the approach was recorded. The results suggest that a neglectful maternal parenting style mediates the effect that verbal threat information has on physiological responses. However, a punitive maternal parenting style, maternal warmth, overprotection, and accurate monitoring were not found to have a significant effect. Paternal parenting styles were not found to have any significant effect. This experiment adds to the existing evidence demonstrating that parenting practices can mediate components of acquired anxiety emotions.
Properties of Wolf-Rayet Stars
Authors: Crowther Paul A.
Published: June 2008

A review of recent progress relating to Wolf-Rayet (WR) stars is presented. Topics include improved Milky Way statistics from near-IR surveys, different flavours of hydrogen-rich and hydrogen-poor WN stars, WR masses from binary orbits, plus spectroscopic analysis of WR stars resulting in stellar temperatures, luminosities, ionizing fluxes, plus wind properties accounting for clumping. Chemical abundances of WN and WC stars are presented, including a discussion of neon abundances in WC and WO stars fromSpitzerobservations. Empirical evidence supporting metallicity-dependent winds is also presented, including its effect on subtype distributions in different environments. Finally, difficulties in comparisons between evolutionary models and observations are highlighted, plus outstanding issues with predictions from continuous star formation and instantaneous bursts in the Milky Way,
Pulsation-Initiated Mass Loss in Luminous Blue Variables: A Parameter Study
Authors: Onifer Andrew J. , Guzik Joyce A.
Published: June 2008

Luminous blue variables (LBVs) are characterized by semi-periodic episodes of enhanced mass-loss, or outburst. The cause of these outbursts has thus far been a mystery. One explanation is that they are initiated by κ-effect pulsations in the atmosphere caused by a blocking of luminosity at temperatures near the so-called “iron bump” (T ~ 200,000 K), where the Fe opacity suddenly increases and blocks the luminosity. Due to a lag in the onset of convection, the luminosity can build until it exceeds the Eddington limit locally, seeding pulsations and possibly driving some mass from the star. We present preliminary results from a parameter study focusing on the conditions necessary to trigger normal S-Dor type (as opposed to extreme η-Car type) outbursts. We find that as Y increases or Z decreases, the pulsational amplitude decreases and outburst-like behavior, indicated by a large, sudden increase in photospheric velocity, becomes less likely.
Massive Binaries
Authors: Moffat Anthony F. J.
Published: June 2008

As with all binaries, those that contain massive stars reveal various degrees of interaction, depending mainly on orbital separation and age, although things happen much faster in massive binaries. Those massive binaries with initial periods exceeding ~10 years generally only interact via wind-wind collisions, with little or no effect on their subsequent evolution (unless located in dense clusters). Shorter-period systems show even stronger wind-wind collisions as a rule, but also interact more directly via Roche Lobe Overflow or Common Envelope, with dramatic effects on their evolution. If we didn't have binaries among massive stars, we would be missing a whole host of interesting phenomena in the Universe, such as sources of enhanced stellar X-ray or non-thermal radio emission, WR dust-spirals, inverse mass-ratios, very rapid spin, rejuvenation and massive blue-stragglers, enhanced cluster dynamics, many runaways and possibly even SMBHs and GRBs! On the other hand, non(or little)-interacting massive binaries are also useful to provide information on Star-Formation processes and determination of stellar parameters (such as the mass) that would otherwise be difficult or impossible to obtain from single stars. In this review, I highlight some of the developments that have occurred during the past few years since the last IAU Symposium on Massive Stars in 2002.
3-D SPH Simulations of Colliding Winds in η Carinae
Authors: Okazaki Atsuo T. , Owocki Stanley P. , Russell Christopher M. P. , Corcoran Michael F.
Published: June 2008

We study colliding winds in the superluminous binary η Carinae by performing three-dimensional, Smoothed Particle Hydrodynamics (SPH) simulations. For simplicity, we assume both winds to be isothermal. We also assume that wind particles coast without any net external forces. We find that the lower density, faster wind from the secondary carves out a spiral cavity in the higher density, slower wind from the primary. Because of the phase-dependent orbital motion, the cavity is very thin on the periastron side, whereas it occupies a large volume on the apastron side. The model X-ray light curve using the simulated density structure fits very well with the observed light curve for a viewing angle of i = 54° and φ = 36°, where i is the inclination angle and φ is the azimuth from apastron.
The First Determination of the Rotation Rates of Wolf-Rayet Stars
Authors: Chené André-Nicolas , St-Louis Nicole
Published: June 2008

The most recent stellar models have shown that the faster a massive star spins, the more its nuclear yields, mass-loss rate and lifetime are different from the standard model. One thus needs to know the rotation rate of massive stars to trace their evolutionary tracks adequately. In Wolf-Rayet (WR) stars, the direct measurement of the rotational velocity is impossible, since their continuum emission is formed in the dense wind that hides the hydrostatic, stellar surface. Here, we present a technique to derive the rotation rates of WR stars from a periodic wind phenomenon, the corotating interaction regions (CIR). For five WR stars, a first estimate of the rotation rates has been deduced from the CIR periods.
Developments in Physics of Massive Stars
Authors: Meynet Georges , Ekström Sylvia , Maeder André , Hirschi Raphael , Georgy Cyril , Beffa Coralie
Published: June 2008

New constraints on stellar models are provided by large surveys of massive stars, interferometric observations and asteroseismology. After a review of the main results so far obtained, we present new results from rotating models and discuss comparisons with observed features. We conclude that rotation is a key feature of massive star physics.
Rotation and Massive Close Binary Evolution
Authors: Langer Norbert , Cantiello Matteo , Yoon Sung-Chul , Hunter Ian , Brott Ines , Lennon Danny , de Mink Selma , Verheijdt Marcel
Published: June 2008

We review the role of rotation in massive close binary systems. Rotation has been advocated as an essential ingredient in massive single star models. However, rotation clearly is most important in massive binaries where one star accretes matter from a close companion, as the resulting spin-up drives the accretor towards critical rotation. Here, we explore our understanding of this process, and its observable consequences. When accounting for these consequences, the question remains whether rotational effects in massive single stars are still needed to explain the observations.
The Effect of Massive Binaries on Stellar Populations and Supernova Progenitors
Authors: Eldridge John J. , Izzard Robert G. , Tout Christopher A.
Published: June 2008

We have calculated a large set of detailed binary models and used them to test the observed stellar population ratios that compare the relative populations of blue supergiants, red supergiants and Wolf-Rayet stars at different metallicities. We have also used our models to estimate the relative rate of type Ib/c to type II supernovae. We find, with an interacting binary fraction of about two thirds, that we obtain better agreement between our models and observations than with single stars. We discuss the use of models in determining the nature of supernova progenitors and show the surprising result that many type Ib/c supernova progenitors are less luminous and less massive in our models than the observed population of Wolf-Rayet stars.
Thoughts on Core-Collapse Supernova Theory
Authors: Burrows Adam , Dessart Luc , Ott Christian D. , Livne Eli , Murphy Jeremiah
Published: June 2008

An emerging conclusion of theoretical supernova research is that the breaking of spherical symmetry may be the key to the elusive mechanism of explosion. Such explorations require state-of-the-art multi-dimensional numerical tools and significant computational resources. Despite the thousands of man-years and thousands of CPU-years devoted to date to studying the supernova mystery, both require further evolution. There are many computationally-challenging instabilities in the core, before, during, and after the launch of the shock, and a variety of multi-dimensional mechanisms are now being actively explored. These include the neutrino heating mechanism, the MHD jet mechanism, and an acoustic mechanism. The latter is the most controversial, and, as with all the contenders, requires detailed testing and scrutiny. In this paper, we analyze recent attempts to do so, and suggests methods to improve them.
Episodic Mass Loss and Pre-SN Circumstellar Envelopes
Authors: Smith Nathan
Published: June 2008

I discuss observational clues concerning episodic mass-loss properties of massive stars in the time before the final supernova explosion. In particular, I will focus on the mounting evidence that LBVs and related stars are candidates for supernova progenitors, even though current paradigms place them at the end of core-H burning. Namely, conditions in the immediate circumstellar environment within a few 102 AU of Type IIn supernovae require very high progenitor mass-loss rates. Those rates are so high that the only known stars that come close are LBVs during rare giant eruptions. I will highlight evidence from observations of some recent extraordinary supernovae suggesting that explosive or episodic mass loss (a.k.a. LBV eruptions like the 19th century eruption of Eta Car) occur in the 5-10 years immediately preceding the SN. Finally, I will discuss some implications for stellar evolution from these SNe, the most important of which is the observational fact that the most massive stars can indeed make it to the ends of their lives with substantial H envelopes intact, even at Solar metallicity.
The Progenitor Stars of Core-Collapse Supernovae
Authors: Smartt Stephen J. , Crockett R. Mark , Eldridge John J. , Maund Justyn R.
Published: June 2008

Knowledge of the nature and mass of the progenitor stars of core-collapse supernovae are critical elements to test theoretical models of stellar evolution and stellar explosions. Here we describe the current limits and restrictions that can be placed on the progenitor stars of type II SNe and those of Ib/c. There are detections of some type II-P SN progenitors but the exploding stars that produce type Ib/c have eluded discovery. We discuss implications of these quantitative limits and the conclusions that we can now draw.
Can Very Massive Stars Avoid Pair-Instability Supernovae?
Authors: Ekström Sylvia , Meynet Georges , Maeder André
Published: June 2008

Very massive primordial stars (140 M⊙ < M < 260 M⊙) are supposed to end their lives as PISN. Such an event can be traced by a typical chemical signature in low metallicity stars, but at the present time, this signature is lacking in the extremely metal-poor stars we are able to observe. Does it mean that those very massive objects were not formed, contrarily to the primordial star formation scenarios ? Could it be possible that they avoided this tragic fate ?

We explore the effects of rotation, anisotropical mass loss and magnetic field on the core size of very massive Population III models. We find that magnetic fields provide the strong coupling that is lacking in standard evolution metal-free models and our 150 M⊙ Population III model avoids indeed the pair-instability explosion.
Evolution of Progenitor Stars of Type Ibc Supernovae and Long Gamma-Ray Bursts
Authors: Yoon Sung-Chul , Langer Norbert , Cantiello Matteo , Woosley Stan E. , Glatzmaier Gary A.
Published: June 2008

We discuss how rotation and binary interactions may be related to the diversity of type Ibc supernovae and long gamma-ray bursts. After presenting recent evolutionary models of massive single and binary stars including rotation, the Tayler-Spruit dynamo and binary interactions, we argue that the nature of SNe Ibc progenitors from binary systems may not significantly differ from that of single star progenitors in terms of rotation, and that most long GRB progenitors may be produced via the quasi-chemically homogeneous evolution at sub-solar metallicity. We also briefly discuss the possible role of magnetic fields generated in the convective core of a massive star for the transport of angular momentum, which is potentially important for future stellar evolution models of supernova and GRB progenitors.
Young Massive Clusters
Authors: Figer Donald F.
Published: June 2008

Over the past ten years, there has been a revolution in our understanding of massive young stellar clusters in the Galaxy. Initially, there were no known examples having masses >104, yet we now know that there are at least a half dozen such clusters in the Galaxy. In all but one case, the masses have been determined through infrared observations. Several had been identified as clusters long ago, but their massive natures were only recently determined. Presumably, we are just scratching the surface, and we might look forward to having statistically significant samples of coeval massive stars at all important stages of stellar evolution in the near future. I review the efforts that have led to this dramatic turn of events and the growing sample of young massive clusters in the Galaxy.
Massive Stars in the Galactic Center
Authors: Martins F. , Hillier D. J. , Genzel R. , Eisenhauer F. , Ott T. , Gillessen S. , Trippe S.
Published: June 2008

We present results of two studies aiming at better understanding the properties of massive stars in the Galactic Center. We focus on the youngest and oldest of the three massive clusters harboring this region, namely the Arches and central cluster. We show that the development of powerful observational techniques in the near infrared spectral range (mainly 3D spectroscopy) allows to uncover the entire massive star population in these clusters. Using CMFGEN models, we derive the classical stellar and wind properties of 46 stars, as well as their surface abundances. The latter allow us to investigate in detail their evolutionary status and to identify evolutionary sequences between different types of stars. We thus constrain stellar evolution in the upper part of the HR diagram.
Massive Stars in the Nuclei and Arms of Spirals
Authors: Bresolin Fabio
Published: June 2008

Many of the properties of massive stars in external galaxies, such as chemical compositions, mass functions, and ionizing fluxes, can be derived from the study of the associated clouds of ionized gas. Moreover, the signatures of Wolf-Rayet stars are often detected in the spectra of extragalactic H ii regions. This paper reviews some aspects of the recent work on the massive star content of nearby spiral galaxies, as inferred from the analysis of giant H ii regions. Particular attention is given to regions of high metallicity, including nuclear hot spots, and to the chemical abundance comparison between supergiant stars and ionized gas.
Extragalactic Stellar Astronomy with the Brightest Stars in the Universe
Authors: Kudritzki Rolf , Urbaneja Miguel A. , Bresolin Fabio , Przybilla Norbert
Published: June 2008

A supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest “normal” stars at visual light with absolute visual magnitudes up to −9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure accurate extragalactic distances based on the stellar gravities and effective temperatures is presented, the flux weighted gravity – luminosity relationship (FGLR). The FGLR is a purely spectroscopic method, which overcomes the uncertainties introduced by interstellar extinction and variations of metallicity, which plague all photometric stellar distance determination methods. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.
LBT Discovery of a Yellow Supergiant Eclipsing Binary in the Dwarf Galaxy Holmberg IX
Authors: Prieto J. L. , Stanek K. Z. , Kochanek C. S. , Weisz D. R.
Published: June 2008

In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (MV ≃ −7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 271 days and the light curve is well-fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed of two yellow supergiants (V − I ≃ 1 mag, Teff = 4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however note a second example. The SMC F0 supergiant R47 is a bright (MV ≃ −7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well-fit as a contact binary with a 181 day period. We propose that these massive systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage.
Infrared Tracers of Mass-Loss Histories and Wind-ISM Interactions in
Hot Star Nebulae
Authors: Morris Patrick ,   the Spitzer WRRINGS team
Published: June 2008

Infrared observations of hot massive stars and their environments provide a
detailed picture of mass loss histories, dust formation, and dynamical
interactions with the local stellar medium that can be unique to the thermal
regime. We have acquired new infrared spectroscopy and imaging with the
sensitive instruments onboard the Spitzer
Space Telescope in guaranteed and open time programs comprised of some of the
best known examples of hot stars with circumstellar nebulae, supplementing with
unpublished Infrared Space Observatory spectroscopy. Here wepresent highlights
of our work on the environment around the extreme P Cygni-type star HDE316285,
providing some defining characteristics of the star's evolution and
interactions with the ISM at unprecented detail in the infrared.
Radiative Feedback in Galaxies
Authors: Oey M. S. , Voges E. S. , Walterbos R. A. M. , Meurer G. R. , Yelda S. , Furst E.
Published: June 2008

We examine the fate of ionizing radiation from massive stars on global scales. First, we compare the observed Hα luminosities of LMC Hii regions with those predicted by the latest generation of stellar atmosphere models. Our results imply that classical Hii regions are on average radiation-bounded, rather than density-bounded, as we found a decade ago. This is likely to necessitate an additional ionizing source for the diffuse, warm ionized medium (WIM) in galaxies. Secondly, we present new results from the SINGG Hα galaxy survey, showing that starburst galaxies have a lower fraction of WIM emission than normal star-forming galaxies. The most intriguing and consequential possible cause for this effect is the escape of ionizing radiation from starbursts. We show that the observations are also consistent with our predictions for the escape of ionizing radiation. Nevertheless, other observations do not necessarily support this scenario and other possible explanations must be considered.
Evidence for a Mass Outflow from Our Galactic Center
Authors: Law Casey
Published: June 2008

We discuss the nature of the Galactic center lobe (GCL), a degree-tall, loop-like structure apparently erupting from the central few hundred parsecs of our Galaxy. Although its coincidence with the Galactic center has inspired diverse models for its origin, the observational evidence connecting this structure to the GC region has been thin. We describe a multiwavelength observing campaign with the VLA, GBT, Spitzer, and other telescopes that finds compelling evidence that the structure is likely formed by a mass outflow from the central tens of parsecs of our Galaxy. The size and mass of the putative outflow is consistent with that expected from the observed supernova rate and gas pressure in the GC region. If the GCL is a mass outflow, its relative proximity offers a unique opportunity for studying these structures in unprecedented detail.
Massive Stars at High Redshifts
Authors: Pettini Max
Published: June 2008

The five years that have passed since the last IAU Symposium devoted to massive stars have seen a veritable explosion of data on the high redshift universe. The tools developed to study massive stars in nearby galaxies are finding increasing application to the analysis of the spectra of star-forming regions at redshifts as high asz= 7. In this brief review, I consider three topics of relevance to this symposium: the determination of the metallicities of galaxies at high redshifts from consideration of their ultraviolet stellar spectra; constraints on the initial mass function of massive stars in galaxies atz= 2 − 3; and new clues to the nucleosynthesis of carbon and nitrogen in massive stars of low metallicity. The review concludes with a look ahead at some of the questions that may occupy us for the next five years (at least!).
Star Forming Galaxies at z > 5
Authors: Taniguchi Yoshi
Published: June 2008

We present recent progress in searching for galaxies at redshift from z ≃ 5 to z ∼ 10. Wide-field and sensitive surveys with 8m class telescopes have been providing more than several hundreds of star forming galaxies at z ∼ 5 − 7 that are probed in the optical window. These galaxies are used to study the early cosmic star formation activity as well as the early structure formation in the universe. Moreover, near infrared deep imaging and spectroscopic surveys have found probable candidates of galaxies from z ∼ 7 to z ∼ 10. Although these candidates are too faint to be identified unambiguously, we human being are now going to the universe beyond 13 billion light years, close to the epoch of first-generations stars; i.e., Population III stars. We also mention about challenges to find Population III-dominated galaxies in the early universe.
Probing the Interstellar Medium and Stellar Environments of Long-Duration GRBs
Authors: Dessauges-Zavadsky Miroslava , Prochaska Jason X. , Chen Hsiao-Wen
Published: June 2008

We review the properties of the gas surrounding high-redshift gamma-ray bursts (GRBs) assessed through the analysis of damped Lyman-alpha systems (DLAs) identified in their afterglow spectra. These GRB-DLAs are characterized by large H I column densities with a median of N(H I) = 1021.7 cm−2, no molecular gas signatures, metallicities ranging from 1/100 to nearly solar with a median exceeding 1/10 solar, and no anomalous abundance patterns. The detection of the atomic Mg lines and the time-variability of the fine-structure lines demonstrates that the majority of the neutral gas along the GRB sightlines is located between 50 pc and a few kpc from the GRB. This implies that this gas is presumably associated with the ambient interstellar medium of the host galaxy and that the derived properties from low-ionization lines do not directly constrain the local environment of the GRB progenitor. The highly ionized gas, traced by N V lines, which could result from a pre-existing H II region produced by the GRB progenitor and neighboring OB stars, appears on the other hand to be very local to the GRB at about 10 pc, yielding a snapshot of the medium's physical conditions at this radius.
The First Stars
Authors: Johnson Jarrett L. , Greif Thomas H. , Bromm Volker
Published: June 2008

The formation of the first generations of stars at redshifts z ≥ 15 − 20 signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding the assembly process of the first galaxies, starting with cosmological initial conditions and modelling the detailed physics of star formation. In particular, we study the role of HD cooling in ionized primordial gas, the impact of UV radiation produced by the first stars, and the propagation of the supernova blast waves triggered at the end of their brief lives. We conclude by discussing how the chemical abundance patterns observed in extremely low-metallicity stars allow us to probe the properties of the first stars.
Imprint of First Stars Era in the Cosmic Infrared Background Fluctuations
Authors: Kashlinsky Alexander
Published: June 2008

We present the latest results on Cosmic Infrared Background (CIB) fluctuations from early epochs from deep Spitzer data. The results show the existence of significant CIB fluctuations at the IRAC wavelengths (3.6 to 8 μm) which remain after removing galaxies down to very faint levels. These fluctuations must arise from populations with a significant clustering component, but only low levels of the shot noise. There are no correlations between the source-subtracted IRAC maps and the corresponding fields observed with the HST ACS at optical wavelengths. Taken together, these data imply that 1) the sources producing the CIB fluctuations are individually faint with Sν < a few nJy at 3.6 and 4.5 μm; 2) have different clustering pattern than the more recent galaxy populations; 3) are located within the first 0.7 Gyr (unless these fluctuations can somehow be produced by - so far unobserved - local galaxies of extremely low luminosity and with the unusual for local populations clustering pattern), 4) produce contribution to the net CIB flux of at least 1-2 nW m−2 sr−1 at 3.6 and 4.5 μm and must have mass-to-light ratio significantly below the present-day populations, and 5) they have angular density of ~ a few per arcsec2 and are in the confusion of the present day instruments, but can be individually observable with JWST.
The Impact of Extremely Large Telescopes on the Study of the Most
Luminous Stellar Objects
Authors: D'Odorico Sandro
Published: June 2008

The potential advantages of the new generation of Extremely Large Telescopes are
briefly summarized. When used in combination with advanced adaptive optics
modules which can substantially remove the effect of atmospheric turbulence at
infrared wavelengths, these telescopes will provide unique capabilities both in
terms of photon collecting power (→2-4 magnitude advantage) and
angular resolution (4-5 times higher than with current 8-10m telescopes). The
instruments under study for the TMT and E-ELT projects are presented and
compared. I discuss the impact of the ELTs on three major science topics:
stellar populations in galaxies to the Virgo distance, chemical abundances of
the brighter stars in nearby galaxies and high redshift SN and GRBs.
Metallicities at the Sites of Nearby SN and Implications for the SN-GRB Connection
Authors: Modjaz Maryam , Kewley L. , Kirshner R. P. , Stanek K. Z. , Challis P. , Garnavich P. M. , Greene J. E. , Kelly P. L. , Prieto J. L.
Published: June 2008

While the broad-lined Type Ic supernovae (SN Ic-bl) associated with long-duration gamma-ray bursts (GRBs) have been studied, we do not fully understand the conditions that lead to each kind of explosion in a massive star. Here we show clues as to the production mechanism of GRBs by comparing the chemical abundances at the sites of 5 nearby (z < 0.25) broad-lined SN Ic that accompany nearby GRBs with those of 12 nearby (z < 0.14) broad-lined SN Ic that have no observed GRBs. We show that the oxygen abundances at the GRB sites are systematically lower than those found near ordinary broad-lined SN Ic. A unique feature of this analysis is that we present new spectra of the host galaxies and analyze the measurements of both samples in the same set of ways, using 3 independent metallicity diagnostics. We demonstrate that neither SN selection effects (SN found via targeted vs. non-targeted surveys) nor the choice of strong-line metallicity diagnostic can cause the observed trend. Though our sample size is small, the observations are consistent with the hypothesis that low metal abundance is the cause of some massive stars becoming SN-GRB. We derive a cut-off metallicity of 0.2−0.6 Z⊙, with the exact value depending on the adopted metallicity scale and solar abundance value.
Blutungsneigung beim Kind
Authors: Hirt A.
Published: June 2008

In dieser Übersichtsarbeit werden einige grundlegende Aspekte der Klinik, des Labors sowie der Betreuung von Kindern mit vermehrter Blutungsneigung diskutiert. Die Ausführungen sollen dem klinisch tätigen Arzt helfen zu entscheiden, wann ein Kind mit einer Blutungsneigung weiter abgeklärt werden sollte, und ihm eine kurze Übersicht über die häufigsten Ursachen einer gestörten Hämostase geben.
Verwahrloste Witwe in Eigentumswohnung mit Geldsorgen und Suizidgedanken. Ein geriatrischer Hausbesuch.
Authors: Wettstein A.
Published: June 2008

Ein Hausbesuch bestätigt die Verwahrlosung einer 78-jährigen Witwe. Die Untersuchung der Hirnleistung ergibt als Ursache eine leichte bis mittelschwere Demenz vom Alzheimertyp. Die gewünschte Spitexbetreuung kann durch die bescheidene Rente nicht finanziert werden. Dank einer Erhöhung der Hypothekarschuld auf 65% des Wertes der Eigentumswohnung kann eine Leibrente erworben werden, mit der sich die Zinsen finanzieren lassen. Dadurch sinkt das Vermögen unter die Freigrenze für selbstbewohntes Wohneigentum. Ergänzungsleistungen zur AHV können zur Finanzierung der hauswirtschaftlichen Spitexleistungen geltend gemacht werden und die Witwe kann in ihrer Wohnung optimal betreut werden.
Climate modes in southern high latitudes and their impacts on Antarctic sea ice
Authors: Yuan Xiaojun , Li Cuihua
Published: June 2008

This study investigates the influence of high‐latitude climate variability on the Antarctic sea ice distribution. The climate variability examined here includes distinct climate modes, such as the Southern Annular Mode (SAM), quasi‐stationary wave‐3 pattern, Pacific South American pattern (PSA) and Semi‐Annual Oscillation (SAO). The results reveal that the largest impact comes from PSA in the Antarctic Dipole (ADP) region of the western hemisphere at the interannual timescale, which is related to the teleconnection of El Niño−Southern Oscillation (ENSO). The wave‐3 pattern also has a strong and similar influence on sea ice in the ADP regions as PSA does, suggesting a positive interaction between PSA and wave‐3 in the region. Measured by correlation coefficients and their significance, SAM has a relatively less significant influence on sea ice than other climate patterns in general, though this global assessment may not apply to particular regions. Sea ice usually responds to large‐scale atmospheric anomalies with a 2‐month delay. The singular value decomposition (SVD) analysis reveals that the coupled relationships between sea ice and atmospheric pressure, temperature, and wind fields are represented by these known climate modes. The leading coupled modes between sea ice and sea level pressure are accountable for 50% to 60% of total squared covariance for all seasons. The leading modes between sea ice and surface air temperature in winter and summer are also accountable for the same amount of total squared covariance. It indicates that these well‐established climate modes/patterns are the dominant factors leading to a strong interaction between the atmosphere and sea ice field in the Antarctic.
Response of the global ocean to Greenland and Antarctic ice melting
Authors: Stammer D.
Published: June 2008

We investigate the transient response of the global ocean circulation to enhanced freshwater forcing associated with melting of the Greenland and Antarctic ice sheets. Increased freshwater runoff from Greenland results in a basin‐wide response of the North Atlantic on timescales of a few years, communicated via boundary waves, equatorial Kelvin waves, and westward propagating Rossby waves. In addition, modified air‐sea interaction plays a fundamental role in setting up the basin‐scale response of the Atlantic circulation in its subpolar and subtropical gyres. In particular, the modified ocean dynamics and thermodynamics lead to a depression in the central North and South Atlantic that would not be expected from linear wave dynamics. Moreover, the heat content increases on basin and global scales in response to anomalous freshwater forcing from Greenland, suggesting that the ocean's response to enhanced freshwater forcing would be a coupled problem. Other parts of the world ocean experience a much slower adjustment in response to Greenland freshwater forcing, communicated via planetary waves, but also involving advective/diffusive processes, especially in the Southern Ocean. Over the 50 years considered here, most of the sea level increase associated with freshwater input from Greenland remains in the Atlantic Ocean. In contrast, ice melting around Antarctica has a much reduced effect on the global ocean. In both cases, none of the basins came to a stationary state during the 50‐year experiment.
Determination of aperture structure and fluid flow in a rock fracture by high‐resolution numerical modeling on the basis of a flow‐through experiment under confining pressure
Authors: Watanabe Noriaki , Hirano Nobuo , Tsuchiya Noriyoshi
Published: June 2008

A numerical model incorporating experimentally determined fracture surface geometries and fracture permeability is proposed for characterizing aperture structures and fluid flow through rock fractures under confining pressures. The model was applied to artificially created granite tensile fractures with varying shear displacements (0–10 mm) and confining pressures (10–100 MPa). The findings of the study were consistent with those obtained previously, which characterized experimentally determined contact areas and changes in shear stress during the shear process. While the confining pressures considered herein are higher than those of previous studies, experimentally obtained fracture permeability is important for understanding subsurface flow, specifically the fluid flow characteristics in aperture structures under different confining pressures. Development of preferential flow paths is observed in all aperture structures, suggesting that the concept of channeling flow is applicable even under high confining pressures, as well as the existence of 3‐D preferential flow paths within the subsurface fracture network.
New directions in water resources management: The role of water pricing policies
Authors: Iglesias Eva , Blanco María
Published: June 2008

Water resources will face increasing competition and higher environmental concerns during this century. To meet these challenges, the new Water Framework Directive has drawn up an integrated framework and established the basic principles for a sustainable water policy in the European Union. The introduction of water prices reflecting the true cost of irrigation is one of its most innovative components. In this paper, a positive mathematical programming model is developed to assess the environmental and socio‐economic impacts of water pricing policies in Spanish irrigated lands. The model interface allows friendly use and easy replication in a large number of irrigation districts, selected throughout the Spanish territory. The model results show the impact on environmental indicators, water consumption, cropping patterns, technology adoption, labor, farmers' income, and the water agency revenues when different scenarios of cost recovery are considered. It is argued that this modeling approach may be used as a management tool to assist in the implementation of the cost recovery approach of the new Water Framework Directive.
Origin of the sheeted dike complex at superfast spread East Pacific Rise revealed by deep ocean crust drilling at Ocean Drilling Program Hole 1256D
Authors: Umino Susumu , Crispini Laura , Tartarotti Paola , Teagle Damon A. H. , Alt Jeffery C. , Miyashita Sumio , Banerjee Neil R.
Published: June 2008

Superfast spread (22 cm/a) upper oceanic crust drilled at Ocean Drilling Program site 1256 comprises a thick sequence of extrusive lavas underlain by a thin region of sheeted dikes. The sheeted dikes at this site are characterized by the intimate association of in situ hyaloclastic fragmentation and hydrothermal alteration. Lithostatic and magmastatic pressure estimates reveal that there is no effective level of neutral buoyancy within the extrusive layer to trap dikes in the crust. This results in a situation that favors the extrusion rather than intrusion of magma. Fractures created by magmas rising in dikes were the loci of intense hydrothermal circulation and provided the pathways for subsequent dike intrusions. Magma‐rich conditions expected for fast spreading ridge segments give rise to a rapid increase in magmatic pressure, which can result in dike intrusion even under only small deviatoric stress. This allows for the emplacement of narrow dikes in the upper crust, with magmas more likely to extrude, and hence the high extrusive/intrusive ratio for Site 1256.
A top‐down and bottom‐up comparison of paleoproductivity proxies: Calcareous nannofossil Sr/Ca ratios and benthic foraminiferal accumulation rates
Authors: Waite A. J. , Gibbs S. J. , Diester‐Haass L. , Rickaby R. E. M. , Billups K.
Published: June 2008

We investigate whether a relationship exists between organic matter production at the sea surface, recorded by nannofossil carbonate Sr/Ca, and its consumption on the seafloor, measured by benthic foraminiferal accumulation rates (BFAR). A mid‐Pliocene (3.67–3.90 Ma) section of Ocean Drilling Program Site 926 in the northwestern tropical Atlantic was sampled, where previous work established that the calcareous nannoplankton assemblages vary with insolation linked changes in surface water productivity. Our results reveal that coarse fraction nannofossil Sr/Ca varies with changes in assemblage composition and may be predominantly controlled by the geochemistry of the warm water oligotrophic genus Discoaster. BFAR also have a positive relationship with Sr/Ca and Discoaster abundances, implying times of relatively low surface water nutrients coincide with enhanced BFAR. This result is in opposition to what one would expect given the assumption of a direct relationship between primary and export production. We speculate that the BFAR are stimulated by enhanced organic carbon export associated with ballasting by nannofossil assemblages dominated volumetrically by large, robust taxa such as Discoaster species. These results highlight the complexity of interpretations of bulk nannofossil Sr/Ca ratios, as well as BFAR data, with respect to paleoproductivity.
Dynamics of core formation and equilibration by negative diapirism
Authors: Samuel H. , Tackley P. J.
Published: June 2008

We investigate dynamically the timing and metal‐silicate equilibration processes during core formation by negative diapirism. Using numerical modeling in 3‐D axisymmetric geometry, we follow the sinking of iron‐rich diapirs through a viscous silicate mantle. We carried out a parameter study in which shear heating as well as several viscous rheologies are considered and systematically varied. General scaling laws are derived for the diapir sinking velocity as well as for the silicate melt generation and distribution around the diapir. Using these scaling laws, we show that metal diapirs of a radius ∼1–100 m, sinking through a partially molten silicate mantle can chemically equilibrate within the timescales suggested by geochemical constraints. Therefore negative diapirism can contribute significantly to metal‐silicate equilibration processes during core formation.
Strontium isotope constraints on fluid flow in the sheeted dike complex of fast spreading crust: Pervasive fluid flow at Pito Deep
Authors: Barker A. K. , Coogan L. A. , Gillis K. M. , Weis D.
Published: June 2008

Fluid flow through the axial hydrothermal system at fast spreading ridges is investigated using the Sr‐isotopic composition of upper crustal samples recovered from a tectonic window at Pito Deep (NE Easter microplate). Samples from the sheeted dike complex collected away from macroscopic evidence of channelized fluid flow, such as faults and centimeter‐scale hydrothermal veins, show a range of 87Sr/86Sr from 0.7025 to 0.7030 averaging 0.70276 relative to a protolith with 87Sr/86Sr of ∼0.7024. There is no systematic variation in 87Sr/86Sr with depth in the sheeted dike complex. Comparison of these new data with the two other localities that similar data sets exist for (ODP Hole 504B and the Hess Deep tectonic window) reveals that the extent of Sr‐isotope exchange is similar in all of these locations. Models that assume that fluid‐rock reaction occurs during one‐dimensional (recharge) flow lead to significant decreases in the predicted extent of isotopic modification of the rock with depth in the crust. These model results show systematic misfits when compared with the data that can only be avoided if the fluid flow is assumed to be focused in isolated channels with very slow fluid‐rock exchange. In this scenario the fluid at the base of the crust is little modified in 87Sr/86Sr from seawater and thus unlike vent fluids. Additionally, this model predicts that some rocks should show no change from the fresh‐rock 87Sr/86Sr, but this is not observed. Alternatively, models in which fluid‐rock reaction occurs during upflow (discharge) as well as downflow, or in which fluids are recirculated within the hydrothermal system, can reproduce the observed lack of variation in 87Sr/86Sr with depth in the crust. Minimum time‐integrated fluid fluxes, calculated from mass balance, are between 1.5 and 2.6 × 106 kg m−2 for all areas studied to date. However, new evidence from both the rocks and a compilation of vent fluid compositions demonstrates that some Sr is leached from the crust. Because this leaching lowers the fluid 87Sr/86Sr without changing the rock 87Sr/86Sr, these mass balance models must underestimate the time‐integrated fluid flux. Additionally, these values do not account for fluid flow that is channelized within the crust.
Penetration of magnetospheric electric fields to the equator during a geomagnetic storm
Authors: Kikuchi Takashi , Hashimoto Kumiko K. , Nozaki Kenro
Published: June 2008

Penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 November 2001, by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator, Yap (−0.3° GML) and low latitude, Okinawa (14.47° GML). The penetrated electric field caused the DP2 currents at the equator, i.e., eastward currents during the main phase of the storm, while the overshielding currents, i.e., westward currents dominated during the recovery phase. It is shown that the ring current started to develop simultaneously with the onset of the equatorial DP2 within the temporal resolution of a few minutes. These results imply prompt transmission of the dawn‐to‐dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere. It is found that the equatorial DP2 started to decrease one hour after the onset of the ring current development, indicating shielding effects becoming effective at the equator during the latter half of the storm main phase. The DP2 was then overwhelmed by the overshielding, which resulted in the counter electrojet (CEJ) in the beginning of the storm recovery phase. The IMAGE magnetometer chain data indicate that the westward auroral electrojet (AEJ) in the dawn sector was driven over midlatitude centered at 57° corrected geomagnetic latitude (CGML) during the main phase, while the AEJ shifted rapidly poleward to the auroral latitude centered at 67° CGML in the beginning of the recovery phase. The overshielding must be caused by the abrupt poleward shift of the R1 FACs as inferred from the poleward shift of the AEJ, in addition to the decrease in their magnitude due to the decrease in magnitude of the southward IMF. The geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2.7 as compared with the geomagnetic storm at low latitude. This amplification is a result of both effects of the DP2 currents and the CEJ associated with the main and recovery phases, respectively. It is suggested that the electric field associated with the DP2 currents contributed to the development of the ring current during the main phase, while the overshielding electric field may contribute to cease developing the ring current during the recovery phase.
Probability distributions of electron precipitation at high magnetic latitudes
Authors: Hardy D. A. , Holeman E. G. , Burke W. J. , Gentile L. C. , Bounar K. H.
Published: June 2008

We have integrated more than 600 million energetic electron spectra measured by the Special Sensor for Precipitating Particles, version 4 (SSJ4) sensor on nine Defense Meteorological Satellite Program (DMSP) spacecraft to obtain total number fluxes (Jtot [#/cm2 s sr]) and energy fluxes (JEtot [keV/cm2 s sr]). These quantities were first separated into bins of 1° in magnetic latitude (MLat), 1 h in magnetic local time (MLT) and unit steps of Kp and then into 26 × 26 logarithmically‐spaced matrices covering the ranges 104 to 1010.25 for JEtot and Jtot and 10−3 to 103.25 for average energy EAVE. Joint probability densities were then calculated as ratios of the number of samples within a matrix element to the total samples in each MLat‐MLT‐Kp bin. Our analysis shows that (1) in all bins probabilities for detecting any of the three parameters were lognormally distributed, and (2) in most bins distributions were multimodal. Measured multimodal probability distributions are well represented as superpositions of contributions from as many as four lognormal populations. These distributions have inherent positive skews with significant separations between their mean and most probable values. Average values of JEtot and EAVE now widely used to model distributions of auroral conductance at different levels of Kp are verified in the large DMSP data set. However, the lognormal and multimodal characters of their realizations in nature indicate that probabilities of detecting them at a given time in a MLat‐MLT‐Kp bin never exceed 10%.