bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating Pulse Morphology in GX 1+4
Authors: Storey Michelle C. , Greenhill J. G. , Kotani T. 
Published: March 2011

AbstractObservational and theoretical evidence points to the existence of an unusually high magnetic field on GX 1+4. The pulsar is thus an ideal laboratory for studying two-photon cyclotron emission, an important source of photons of frequency significantly less than the cyclotron frequency in X-ray pulsars. Low-frequency approximations to the two-photon cyclotron emission transition probabilities are derived. These are used to calculate the theoretical opening angle of the double-humped pulse shape predicted by the two-photon cyclotron emission model. The theoretical pulse shape, incorporating the effects of gravitational light bending, is compared with observations of GX 1+4. Observed light curves have opening angles consistent with the theoretically predicted maximum value.
An Analytic Flow Solution for YSO Jets
Authors: Liffman Kurt 
Published: March 2011

AbstractWe present an analytic solution for a jet flow from a young stellar object (YSO). This solution allows us to compute the speed, density, and magnetic field strength of the flow, but it is only true if YSO jet flows are powered by toroidal magnetic fields. We illustrate how the balance between centrifugal force and magnetic pressure provides the converging/diverging nozzle shape required to accelerate the flow.
Identification of Two z ~ 3·8 QSOs in a Deep CCD Survey
Authors: Smail Ian , Edge Alastair C. , Ellis Richard S. 
Published: March 2011

AbstractWe present the identifications of two z ~ 3·8 quasars from a deep UBI imaging survey with the Palomar 5·1 m Telescope. The survey covers an area of 0·25 degree2 around a sample of ten z =0·2–0·3 luminous X-ray clusters. The QSOs were identified on the basis of their stellar morphologies, relatively blue optical and very red UV–optical colours. The two objects are Q 1322+5034, with total magnitudes of B =20·8, I =18·3 and (U–B) > 4·7, and Q 1722+3211, which has total magnitudes of B =21·8, I =19·7 and (U–B) > 3·2. Subsequent spectroscopic observations with the 4·2 m William Herschel Telescope have confirmed the identity of these two sources as QSOs at z =3·82 and z =3·73 respectively. Our spectroscopic observations identify a damped Lyman-α absorber in the spectrum of Q 1322+5034 at z =3·439, as well as a second absorption system at z =2·700, which may be either a single very high column density, damped Lyman-α system, or more likely a blend of a number of high column-density absorbers spread over a distance of ~10 Mpc.
Obscuration by Diffuse Cosmic Dust
Authors: Masci Frank J. 
Published: March 2011

AbstractIf the background universe is observed through a significant amount of diffusely distributed foreground dust, then studies at optical wavelengths may be severely biased. Previous studies investigating the effects of foreground dust on background sources assumed dust to be ‘compactly’ distributed, i.e. on scales comparable to the visible extent of normal galaxies. We show, however, that diffuse dust is more effective at obscuring background sources. Galaxy clusters are a likely location for ‘large-scale’ diffusely distributed dust, and its effect on the counts of background sources is explored. We also explore the implications of a hypothesised diffuse intergalactic dust component uniformly distributed to high redshift with comoving mass density equal to that associated with local galaxies. In this case, we predict a deficit in background sources about three times greater than that found in previous studies.
Singularities in a Relativistic Pulsar Wind
Authors: Li Jianke 
Published: March 2011

AbstractThe nature of a singularity in a cool, gravitation-free axisymmetrical, relativistic, steady pulsar wind is further investigated, in line with the recent counter-argument of Ardavan (1995, hereafter A95) that the pure Alfvén ‘singularity’ has an equal importance to the Alfvén singularity if one defines the singularity via a quadratic form rather than using the ratio as adopted by Li & Melrose (1994). The pure Alfvénic point in A95 coincides with the proposed characteristic point through which a continuous wind will meet the star and infinity. However, we find that the critical point as implied in the quadratic form is in fact the intermediate point (Ardavan 1979), but not the pure Alfvénic point. Thus the analysis of A95 does not indicate any significance of the pure Alfvénic point. We also demonstrate that the intermediate point which appears in the quadratic form of A95 is not genuine.
Simulating AXAF Grating Spectra of Accreting White Dwarfs
Authors: Tennant Allyn F. , Wu Kinwah , O'Dell Stephen L. , Weisskopf Martin C. 
Published: March 2011

AbstractWe present simulated AXAF spectra of accreting white dwarfs, using parameters appropriate for magnetic cataclysmic variables. The very high spectral resolution that can be obtained with the High-Energy Transmission Grating of AXAF can resolve the keV X-ray emission lines that characterise the temperature, density and velocity profiles of the shock-heated emission regions of these systems. These simulations demonstrate that actual spectra will allow us to place constraints on the white-dwarf mass and the accretion rate of the systems. The high-resolution spectra also allow the measurement of the velocity of the accretion flow in regions close to the white-dwarf surface.
HI in Early-type Galaxies
Authors: Oosterloo Tom , Morganti Raffaella , Sadler Elaine 
Published: March 2011

AbstractWe summarise the HI properties of early-type galaxies, in particular the differences in HI morphologies observed in early-type galaxies of different luminosities. We find that in low-luminosity early-type galaxies the HI is almost always in a disk-like structure, with central surface densities high enough for star formation to occur. In a few luminous early-type galaxies the HI is also in a disk or in a ring-like structure, but in most luminous early-type galaxies the HI has a relatively irregular morphology. The surface densities in the HI disks in luminous early-type galaxies are lower than in the HI disks in low-luminosity early-type galaxies and no large-scale star formation should occur in these disks. We discuss these different HI characteristics in the context of other properties of early-type galaxies that correlate with luminosity.
First Results from the Parkes Multibeam High-velocity Cloud Survey
Authors: Putman M. E. , Gibson B. K. 
Published: March 2011

AbstractWith the onset of the HI Parkes All-Sky Survey (HIPASS), a new view of the high-velocity cloud (HVC) distribution in the southern sky is being revealed. The dense spatial sampling and unbiased coverage of HIPASS gives it multiple advantages over previous surveys of the southern sky. Detailed views of the clouds' structure and large mosaics of the HI sky allow us to link individual concentrations to larger structures (such as the Magellanic Clouds and the Galaxy), providing pictorial clues as to the origins of HVCs. It is clear that HVCs cannot be uniformly assigned a single origin scenario, and must be categorised appropriately.
The Low-redshift Intergalactic Medium
Authors: Shull J. Michael , Penton Steven V. , Stocke John T. 
Published: March 2011

AbstractThe low-redshift Lyα forest of absorption lines provides a probe of large-scale baryonic structures in the intergalactic medium, some of which may be remnants of physical conditions set up during the epoch of galaxy formation. We discuss our recent Hubble Space Telescope (HST) observations and interpretation of low-z Lyα clouds toward nearby Seyferts and QSOs, including their frequency, space density, estimated mass, association with galaxies, and contribution to Ωb. Our HST/GHRS detections of ∼ 70 Lyα absorbers with Nhi ≥ 1012·6 cm−2 along 11 sightlines covering pathlength Δ(cz) = 114,000 km s−1 show f (>Nhi) α Nhi−0·63±0·04 and a line frequency dN/dz = 200 ± 40 for Nhi > 1012·6 cm−2 (one every 1500 km s−1 of redshift). A group of strong absorbers toward PKS 2155–304 may be associated with gas (400–800) kpc from four large galaxies, with low metallicity (≤0·003 solar) and D/H ≤ 2 × 10−4. At low-z, we derive a metagalactic ionising radiation field from AGN of J0 = × 10−23 erg cm−2 s−1 Hz−1 sr−1 and a Lyα-forest baryon density Ωb =(0·008 ± 0·004)[J−23N14b100]½ for clouds of characteristic size b = (100 kpc)b100.
HI Column Density Distribution Function at z = 0: Connection to Damped Lyα Statistics
Authors: Zwaan Martin A. , Verheijen Marc A. W. , Briggs Frank H. 
Published: March 2011

AbstractWe present a measurement of the HI column density distribution function f(Nhi) at the present epoch for column densities > 1020 cm−2. These high column densities compare to those measured in damped Lyα lines seen in absorption against background quasars. Although observationally rare, it appears that the bulk of the neutral gas in the Universe is associated with these damped Lyα systems. In order to obtain a good anchor point at z = 0 we determine f(Nhi) in the local Universe by using 21 cm synthesis observations of a complete sample of spiral galaxies. We show that f(Nhi) for damped Lyα systems has changed significantly from high z to the present and that change is greatest for the highest column densities. The measurements indicate that low surface brightness galaxies make a minor contribution to the cross section for HI, especially for NHI > 1021 cm−2.
The Violent Interstellar Medium of Nearby Dwarf Galaxies
Authors: Walter Fabian 
Published: March 2011

AbstractHigh resolution HI observations of nearby dwarf galaxies (most of which are situated in the M81 group at a distance of about 3·2 Mpc) reveal that their neutral interstellar medium (ISM) is dominated by hole-like features most of which are expanding. A comparison of the physical properties of these holes with the ones found in more massive spiral galaxies (such as M31 and M33) shows that they tend to reach much larger sizes in dwarf galaxies. This can be understood in terms of the galaxy's gravitational potential. The origin of these features is still a matter of debate. In general, young star forming regions (OB-associations) are held responsible for their formation. This picture, however, is not without its critics and other mechanisms such as the infall of high velocity clouds, turbulent motions or even gamma ray bursters have been recently proposed. Here I will present one example of a supergiant shell in IC 2574 which corroborates the picture that OB associations are indeed creating these structures. This particular supergiant shell is currently the most promising case to study the effects of the combined effects of stellar winds and supernova explosions which shape the neutral interstellar medium of (dwarf) galaxies.
A Constraint on the Standard Beaming Model for Superluminal Sources
Authors: Ubachukwu A. 
Published: March 2011

AbstractWe have used two subsamples of superluminal quasars to test the relativistic beaming model, and to place useful constraints on the radio source orientation hypothesis and cosmology. Based on the variation of the observed ratio R of the core-to-lobe radio luminosities with proper motion μ for the subsample of lobe-selected quasars, we show that the observed R–μ data can be explained in terms of a bulk relativistic motion with Lorentz factor γ≈4. Also, from the observed proper motion versus redshift (μ–z) plot for this subsample, we show that γ≈4 implies a high density universe with deceleration parameter q0 = 0·5. Furthermore, from the observed (μ–z) plot for the two subsamples taken separately, we show that both γ and μ for the core-selected subsample exceed those of the lobe-selected subsample by a factor of 2 for the q0 = 0·5 world model. This result is demonstrated to be consistent with an orientation-based unified scheme in which lobe-selected quasars lie, on the average, at an angle which is a factor of ∼2–3 larger than that of their core-selected counterparts.
Two New Planetary Nebulae and an AGN in the Galactic Plane
Authors: Beer S. H. , Vaughan A. E. 
Published: March 2011

AbstractA search for planetary nebulae was carried out using candidates selected by their infrared colours and 5 GHz radio emission. One new planetary nebula was identified on the basis of its small angular size, strong [O iii] emission and infrared colours. Another object, known as the possible planetary nebula Wray 16–28, is similarly identified as a planetary nebula. An undiscovered AGN was also found, and is classed as a Seyfert 2 galaxy on the basis of its strong O iii emission, linewidths of ∼500 km s−1, and 5 GHz radio flux. Low-resolution optical spectra are presented and distance estimates discussed.
Summary of the ‘Sub-microJansky Radio Sky’ Workshop
Authors: Hopkins Andrew , Ekers Ron , Jackson Carole , Cram Lawrence , Green Anne , Manchester Dick , Staveley-Smith Lister , Norris Ray 
Published: March 2011

AbstractThe Square Kilometre Array Radio Telescope is the next generation radio telescope. An international project is currently under way to design and build an instrument having an effective collecting area two orders of magnitude greater than that of any existing telescope. A number of separate studies are presently investigating how to design the Square Kilometre Array to best carry out the kinds of observations desired by the astronomical community. We present a summary of one of these studies, a workshop called The ‘Sub-microJansky Radio Sky’ held at the ATNF, Sydney, on 17 June 1998. This workshop addressed the nature of the radio sky at the very faint flux densities likely to be attainable by the Square Kilometre Array. In particular, each speaker investigated a separate population of radio sources and how the expected appearance of that population at such faint flux densities would dictate how to refine some of the design constraints for the Square Kilometre Array.
Photohadronic Processes in Astrophysical Environments
Authors: Mücke A. , Rachen J. P. , Engel Ralph , Protheroe R. J. , Stanev Todor 
Published: March 2011

AbstractWe discuss the first applications of our newly developed Monte Carlo event generator SOPHIA to multiparticle photoproduction of relativistic protons with thermal and power-law radiation fields. The measured total cross section is reproduced in terms of excitation and decay of baryon resonances, direct pion production, diffractive scattering, and non-diffractive multiparticle production. Non-diffractive multiparticle production is described using a string fragmentation model. We demonstrate that the widely used ‘Δ-approximation’ for the photoproduction cross section is reasonable only for a restricted set of astrophysical applications. The relevance of this result for cosmic ray propagation through the microwave background and hadronic models of active galactic nuclei and gamma-ray bursts is briefly discussed.
Comets and Communication: Amateur–Professional Tension in Australian Astronomy
Authors: Orchiston Wayne 
Published: March 2011

AbstractAustralasian amateur astronomers, Grigg and Ross, discovered four different comets between 1902 and 1907. Controversy surrounding these discoveries led to a deterioration in relations between Australia's leading amateur astronomers and Baracchi at Melbourne Observatory, and to the eventual transfer of the ‘Australian Central Bureau’ to Sydney Observatory.
Magnetic Fields in Accretion Disks
Authors: de Kool Marthijn , Bicknell Geoffrey V. , Kuncic Zdenka 
Published: March 2011

AbstractThis paper summarises our work on the role of magnetic fields in accretion disks presented in two papers elsewhere. In the first part (a summary of part of Kuncic & Bicknell 1999), we present a formal development of the equations governing the structure of an accretion disk containing magnetohydrodynamic turbulence. The importance of the different terms in the energy and momentum equations is discussed, and a parametrisation of the unresolved processes is suggested that could be used to make further progress. We briefly explore whether an MHD accretion disk can transport a significant part of the gravitational power into a corona by buoyancy. In the second part, we present some exploratory calculations of the vertical structure of accretion disks, in which non-local dissipation of energy due to the buoyant transport of magnetic field energy is taken into account. It is argued that the efficiency of buoyant magnetic transport depends very strongly on the size of the coherent magnetic regions. If the size of the buoyant cells is not very close to the disk thickness, magnetic energy generated by dynamo action inside the disk will be dissipated locally, and will not be available to transport a significant part of the accretion luminosity into a corona.
The Cloudy Universe
Authors: Walker Mark , Wardle Mark 
Published: March 2011

AbstractModelling of extreme scattering events suggests that the Galaxy's dark matter is an undetected population of cold, AU-sized, planetary-mass gas clouds. None of the direct observational constraints on this picture—thermal/non-thermal emission, extinction and lensing—are problematic. The theoretical situation is less comfortable, but still satisfactory. Galactic clouds can survive in their current condition for billions of years, but we do not have a firm description for either their origin or their evolution to the present epoch. We hypothesise that the proto-clouds formed during the quark–hadron phase transition, thereby introducing the inhomogeneity necessary for compatibility with light element nucleosynthesis in a purely baryonic universe. We outline the prospects for directly detecting the inferred cloud population. The most promising signatures are cosmic-ray-induced Hα emission from clouds in the solar neighbourhood, optical and X-ray flashes arising from cloud–cloud collisions, ultraviolet extinction, and three varieties of lensing phenomena.
On some constants for oscillation and stability of delay equations
Authors: Berezansky Leonid , Braverman Elena 
Published: March 2011

We discuss the famous constants of1/e1/e, 1,3/23/2in necessary and/or sufficient oscillation and stability conditions for delay differential equations with one or more delays:\[x′(t)=−∑k=1mak(t)x(t−hk(t)),x^{\prime }(t)= - \sum _{k=1}^ma_k(t) x(t-h_k(t)),\]including equations with oscillatory coefficients. Some counterexamples (which refer to necessary oscillation and stability conditions) are presented and open problems are stated.
Remifentanil as single agent to facilitate awake fibreoptic intubation in the absence of premedication*
Authors: Vennila R. , Hall A. , Ali M. , Bhuiyan N. , Pirotta D. , Raw D. A. 
Published: March 2011

SummaryRemifentanil is increasingly being used as the primary agent to provide sedation during awake fibreoptic nasal intubation. In this observational study, we aimed to determine the optimal effect site concentration of remifentanil, using a target controlled infusion based on the Minto pharmacological model, to provide optimal safe intubation conditions without the use of other sedatives/premedication and/or spray‐as‐you‐go local anaesthesia. Twenty patients with anticipated difficult airway participated in the study. Good intubating conditions were achieved in all patients with mean (SD) effect site concentration of 6.3 (3.87) ng.ml−1 of remifentanil recorded at nasal endoscopy and 8.06 (3.52) ng.ml−1 during tracheal intubation. No serious adverse event occurred during any of these procedures. These preliminary findings suggest that this is a feasible and safe technique for awake fibreoptic nasal intubation.
An exploration of parents' and young people's perspectives of hospice support
Authors: Kirk S. , Pritchard E. 
Published: March 2011

AbstractBackground  Hospices are an important component of children's palliative care provision and increasing numbers of children/young people with life‐limiting conditions mean that the demand placed on them for support is likely to increase. However, there has been a lack of published research examining how families experience the support provided by children's hospices.Methods  The aim of the study was to investigate parents' and young people's perceptions of hospice support and identify how support could be improved. A mixed‐method approach was used involving a postal survey of families and in‐depth qualitative interviews with a purposively sampled subsample of parents and young people.Results  A total of 108 (49.8% response rate) questionnaires were returned and interviews were conducted with 12 parents and seven young people. Families were highly satisfied with the support provided in terms of quality of care; interpersonal qualities of the staff; the individualized, family‐focused approach; accessibility of support and involvement in decision making. Young people valued the opportunity to meet with other young people and take part in different activities. For parents the provision of a break from caring was the main way in which they were supported although they felt they wanted more of this form of support. A consistent theme in relation to support for young people and siblings was the need to develop facilities, activities and bereavement support specifically for teenagers/young people.Conclusions  Parents value a model of care that provides holistic, family‐focused support that is responsive to individual needs and which promotes control and active involvement in decision making. The key challenge now is to respond to increasing need and a changing population of users.
Comparison of the prevalence and impact of health problems of pre‐school children with and without cerebral palsy
Authors: Wong C. , Bartlett D. J. , Chiarello L. A. , Chang H‐J. , Stoskopf B. 
Published: March 2011

AbstractBackground  The range of health problems associated with children with cerebral palsy (CP) is well documented in the literature; however, the existing data are often either reported for samples of children with all types of CP, or stratified by typology of motor disorder, rather than using the Gross Motor Function Classification System (GMFCS), which has been shown to be the most reliable way of classifying children with CP. Furthermore, availability of research on pre‐school‐aged children (under 5 years) is sparse. The aim of this study is to compare the prevalence and impact of health problems in pre‐school children with and without CP, stratified by the GMFCS.Methods  Parents of 430 pre‐school‐aged children with CP (243 boys, 187 girls; mean age = 3 years 2 months, SD = 11 months) and 107 typically developing (TD) children (56 boys, 51 girls; mean age = 3 years 4 months, SD = 11 months) participated. Using the consensus definition of CP and the World Health Organization's International Classification of Functioning, Disability and Health, a parent survey was developed to assess the prevalence and impact of 16 health problems. The measure demonstrates good test–retest reliability (ICC > 0.80) and discriminant validity across GMFCS levels (P < 0.001).Results  Both the prevalence and impact of health problems is greater in children with CP compared with TD children (P < 0.001). The number and impact of health problems increase with ascending GMFCS level (P≤ 0.01), except for the impact of health problems between groups GMFCS I and GMFCS II/III (P= 0.19). Children with CP have an average of between 3.4 and 6.7 health problems, compared with fewer than one in TD children.Conclusions  Service providers working with pre‐school‐aged children with CP need to consider health problems and their impact when planning care.