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Search Results: 1 - 10 of 290837 matches for " Neil E. B. Killeen "
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Cosmological Halos: A Search for the Ionized Intergalactic Medium
Robert M. Geller,Robert J. Sault,Robert Antonucci,Neil E. B. Killeen,Ron Ekers,Ketan Desai
Physics , 1998,
Abstract: Standard big bang nucleosynthesis predicts the average baryon density of the Universe to be a few percent of the critical density. Only about one tenth of the predicted baryons have been seen. A plausible respository for the missing baryons is in a diffuse ionized intergalactic medium (IGM). In an attempt to measure the IGM we searched for Thomson-scattered halos around strong high redshift radio sources. Observations of the radio source 1935-692 were made with the Australia Telescope Compact Array. We assumed a uniform IGM, and isotropic steady emission of 1935-692 for a duration between 10^7 - 10^8 years. A model of the expected halo visibility function was used in \chi^2 fits to place upper limits on \Omega_{IGM}. The upper limits varied depending on the methods used to characterize systematic errors in the data. The results are 2/sigma limits of \Omega_{IGM} < 0.65. While not yet at the sensitivity level to test primordial nucleosynthesis, improvements on the technique will probably allow this in future studies.
The multi-modal Australian ScienceS Imaging and Visualization Environment (MASSIVE) high performance computing infrastructure: applications in neuroscience and neuroinformatics research
Wojtek J. Goscinski,Paul McIntosh,Christopher J. Hall,Darren Thompson,Graham Galloway,Neil E. B. Killeen,Parnesh Raniga,Amanda Ng,Govinda Poudel,David G. Barnes,Toan Nguyen,Paul Bonnington,Gary F. Egan
Frontiers in Neuroinformatics , 2014, DOI: 10.3389/fninf.2014.00030
Abstract: The Multi-modal Australian ScienceS Imaging and Visualization Environment (MASSIVE) is a national imaging and visualization facility established by Monash University, the Australian Synchrotron, the Commonwealth Scientific Industrial Research Organization (CSIRO), and the Victorian Partnership for Advanced Computing (VPAC), with funding from the National Computational Infrastructure and the Victorian Government. The MASSIVE facility provides hardware, software, and expertise to drive research in the biomedical sciences, particularly advanced brain imaging research using synchrotron x-ray and infrared imaging, functional and structural magnetic resonance imaging (MRI), x-ray computer tomography (CT), electron microscopy and optical microscopy. The development of MASSIVE has been based on best practice in system integration methodologies, frameworks, and architectures. The facility has: (i) integrated multiple different neuroimaging analysis software components, (ii) enabled cross-platform and cross-modality integration of neuroinformatics tools, and (iii) brought together neuroimaging databases and analysis workflows. MASSIVE is now operational as a nationally distributed and integrated facility for neuroinfomatics and brain imaging research.
HI and dark matter in the windy starburst dwarf galaxy NGC1705
Gerhardt R. Meurer,Lister Staveley-Smith,N. E. B. Killeen
Physics , 1998, DOI: 10.1046/j.1365-8711.1998.01905.x
Abstract: We present 21cm HI line observations of the blue compact dwarf galaxy NGC1705. Previous optical observations show a strong outflow powered by an ongoing starburst dominating the HII morphology and kinematics. In contrast, most of the HI lies in a rotating disk. An extraplanar HI spur accounts for ~ 8% of the total HI mass, and is possibly associated with the HII outflow. The inferred mass loss rate out of the galaxy's core is significant ~ 0.2 - 2 M_sun/yr, but does not dominate the HI dynamics. Mass model fits to the rotation curve show that the dark matter (DM) halo is dominant at nearly all radii and has a central density \rho_0 \approx 0.1 M_sun/pc^3: ten times higher than typically found in dwarf irregular galaxies, but similar to the only other mass-modelled blue compact dwarf, NGC2915. This large difference strongly indicates that there is little evolution between dwarf irregular and blue compact dwarf types. Instead, dominant DM halos may regulate the morphology of dwarf galaxies by setting the critical surface density for disk star formation. Neither our data nor catalogue searches reveal any likely external trigger to the starburst in NGC1705.
Centaurus A: multiple outbursts or bursting bubble?
R. Morganti,N. E. B. Killeen,R. D. Ekers,T. A. Oosterloo
Physics , 1999, DOI: 10.1046/j.1365-8711.1999.02622.x
Abstract: We present new radio observations of the brighter region of the northern lobe (the Northern Middle Lobe, NML) of Centaurus A obtained at 20 cm with the Australia Telescope Compact Array. The angular resolutions are ~50 and ~130 arcsec, therefore much higher than for the previously available radio images of this region. The most interesting feature detected is a large-scale jet that connects the inner radio lobe and the NML and that is imaged for the first time. The NML itself appears as diffuse emission with a relatively bright ridge on the eastern side. The radio morphology of Centaurus A and, in particular, its NML could be the result of a precessing jet that has undergone a strong interaction with the environment at least in the northern side. The very big drop in intensity between the inner jet and the large-scale jet can be explained with a sequence of bursts of activity at different epochs in the life of the source. Alternatively (or additionally) a ``bursting bubble'' model is proposed which could also explain the good collimation of the large-scale jet. In this model, the plasma accumulated in the inner lobe would be able to ``burst'' out only through one nozzle that would be the region where the large-scale jet forms. From the comparison between the radio emission and the regions of ionized gas we find that the inner optical filament falls about 2 arcmin (~2 kpc) away from the large-scale radio jet. Thus, this filament does not seem to have experienced a direct interaction with the radio plasma. The outer filaments appear to be, in projection, closer to the radio emission, arguing for a direct interaction with the radio jet. However, also in this case a more complicated interaction than assumed so far has to be occuring.
Branch xylem density variations across the Amazon Basin
S. Pati o, J. Lloyd, R. Paiva, T. R. Baker, C. A. Quesada, L. M. Mercado, J. Schmerler, M. Schwarz, A. J. B. Santos, , A. Aguilar, C. I. Czimczik, J. Gallo, V. Horna, E. J. Hoyos, E. M. Jimenez, W. Palomino, J. Peacock, A. Pe a-Cruz, C. Sarmiento, A. Sota, J. D. Turriago, B. Villanueva, P. Vitzthum, E. Alvarez, L. Arroyo, C. Baraloto, D. Bonal, J. Chave, A. C. L. Costa, R. Herrera, N. Higuchi, T. Killeen, E. Leal, F. Luiz o, P. Meir, A. Monteagudo, D. Neil, P. Nú ez-Vargas, M. C. Pe uela, N. Pitman, N. Priante Filho, A. Prieto, S. N. Panfil, A. Rudas, R. Salom o, N. Silva, M. Silveira, S. Soares deAlmeida, A. Torres-Lezama, R. Vásquez-Martínez, I. Vieira, Y. Malhi,O. L. Phillips
Biogeosciences (BG) & Discussions (BGD) , 2009,
Abstract: Xylem density is a physical property of wood that varies between individuals, species and environments. It reflects the physiological strategies of trees that lead to growth, survival and reproduction. Measurements of branch xylem density, ρx, were made for 1653 trees representing 598 species, sampled from 87 sites across the Amazon basin. Measured values ranged from 218 kg m 3 for a Cordia sagotii (Boraginaceae) from Mountagne de Tortue, French Guiana to 1130 kg m 3 for an Aiouea sp. (Lauraceae) from Caxiuana, Central Pará, Brazil. Analysis of variance showed significant differences in average ρx across regions and sampled plots as well as significant differences between families, genera and species. A partitioning of the total variance in the dataset showed that species identity (family, genera and species) accounted for 33% with environment (geographic location and plot) accounting for an additional 26%; the remaining "residual" variance accounted for 41% of the total variance. Variations in plot means, were, however, not only accountable by differences in species composition because xylem density of the most widely distributed species in our dataset varied systematically from plot to plot. Thus, as well as having a genetic component, branch xylem density is a plastic trait that, for any given species, varies according to where the tree is growing in a predictable manner. Within the analysed taxa, exceptions to this general rule seem to be pioneer species belonging for example to the Urticaceae whose branch xylem density is more constrained than most species sampled in this study. These patterns of variation of branch xylem density across Amazonia suggest a large functional diversity amongst Amazonian trees which is not well understood.
Blood culture collection technique and pneumococcal surveillance in Malawi during the four year period 2003–2006: an observational study
Neema Mtunthama, Stephen B Gordon, Temwa Kusimbwe, Eduard E Zijlstra, Malcolm E Molyneux, Neil French
BMC Infectious Diseases , 2008, DOI: 10.1186/1471-2334-8-137
Abstract: A prospective observational study.Following the introduction of a specialised blood culture team in 2005, the proportion of contaminated cultures decreased (19.6% in 2003 to 5.0% in 2006), blood volume cultured increased and pneumococcal recovery increased significantly from 2.8% of all blood cultures to 6.1%. With each extra 1 ml of blood cultured the odds of recovering a pneumococcus increased by 18%.Standardisation and assessment of blood culture performance (blood volume and contamination rate) should be incorporated into pneumococcal disease surveillance activities where routine blood culture practice is constrained by limited resources.Blood cultures are an essential component of good clinical care in the diagnosis and management of blood stream infections (BSI) which are frequent in hospitalised patients in Malawi and the rest of Africa [1-6]. Information from blood culture surveillance is also an important tool for establishing public health priorities, assessing the impact of interventions – particularly vaccines – and for providing information on antimicrobial resistance patterns to help formulate prescribing guidelines for empirical therapy. Blood culture surveillance has been the key tool used in the USA for recognising the enormous potential of childhood pneumococcal conjugate vaccination for decreasing disease in adults[7].In Malawi as in much of the rest of sub-Saharan Africa, blood culture facilities are available in only a limited number of centres. As a consequence single reports are often extrapolated as representative of disproportionately large regions and time periods, and inaccuracies in these reports are more likely to be perpetuated as a result of the lack of alternative data. Blood cultures need to be specific and sensitive and therefore as representative as possible of the true BSI disease burden and particularly so where BSI surveillance is restricted to very few sites.Isolation of bacteria from blood is usually taken as definitive proof
The Clostridium difficile Cell Wall Protein CwpV is Antigenically Variable between Strains, but Exhibits Conserved Aggregation-Promoting Function
Catherine B. Reynolds,Jenny E. Emerson,Lucia de la Riva,Robert P. Fagan,Neil F. Fairweather
PLOS Pathogens , 2011, DOI: 10.1371/journal.ppat.1002024
Abstract: Clostridium difficile is the main cause of antibiotic-associated diarrhea, leading to significant morbidity and mortality and putting considerable economic pressure on healthcare systems. Current knowledge of the molecular basis of pathogenesis is limited primarily to the activities and regulation of two major toxins. In contrast, little is known of mechanisms used in colonization of the enteric system. C. difficile expresses a proteinaceous array on its cell surface known as the S-layer, consisting primarily of the major S-layer protein SlpA and a family of SlpA homologues, the cell wall protein (CWP) family. CwpV is the largest member of this family and is expressed in a phase variable manner. Here we show CwpV promotes C. difficile aggregation, mediated by the C-terminal repetitive domain. This domain varies markedly between strains; five distinct repeat types were identified and were shown to be antigenically distinct. Other aspects of CwpV are, however, conserved. All CwpV types are expressed in a phase variable manner. Using targeted gene knock-out, we show that a single site-specific recombinase RecV is required for CwpV phase variation. CwpV is post-translationally cleaved at a conserved site leading to formation of a complex of cleavage products. The highly conserved N-terminus anchors the CwpV complex to the cell surface. Therefore CwpV function, regulation and processing are highly conserved across C. difficile strains, whilst the functional domain exists in at least five antigenically distinct forms. This hints at a complex evolutionary history for CwpV.
Behavioral variability, elimination of responses, and delay-of-reinforcement gradients in SHR and WKY rats
Espen B Johansen, Peter R Killeen, Terje Sagvolden
Behavioral and Brain Functions , 2007, DOI: 10.1186/1744-9081-3-60
Abstract: The present study investigated behavioral variability and elimination of non-target responses during acquisition in an animal model of ADHD, the spontaneously hypertensive rat (SHR), using Wistar Kyoto (WKY) rats as controls. The study also aimed at providing a novel approach to measuring delay-of-reinforcement gradients in the SHR and the WKY strains. The animals were tested in a modified operant chamber presenting 20 response alternatives. Nose pokes in a target hole produced water according to fixed interval (FI) schedules of reinforcement, while nose pokes in the remaining 19 holes either had no consequences or produced a sound or a short flickering of the houselight. The stimulus-producing holes were included to test whether light and sound act as sensory reinforcers in SHR.Data from the first six sessions testing FI 1 s were used for calculation of the initial distribution of responses. Additionally, Euclidean distance (measured from the center of each hole to the center of the target hole) and entropy (a measure of variability) were also calculated.Delay-of-reinforcement gradients were calculated across sessions by dividing the fixed interval into epochs and determining how much reinforcement of responses in one epoch contributed to responding in the next interval.Over the initial six sessions, behavior became clustered around the target hole. There was greater initial variability in SHR behavior, and slower elimination of inefficient responses compared to the WKY. There was little or no differential use of the stimulus-producing holes by either strain. For SHR, the reach of reinforcement (the delay-of-reinforcement gradient) was restricted to the preceding one second, whereas for WKY it extended about four times as far.The present findings support previous studies showing increased behavioral variability in SHR relative to WKY controls. A possibly related phenomenon may be the slowed elimination of non-operant nose pokes in SHR observed in the present study.
等离子体物理中的计算
B.I.Cohen,J.Killeen,唐福林
力学进展 , 1986, DOI: 10.6052/1000-0992-1986-4-J1986-069
Abstract: 各种大大小小的计算机都有助于完善理论计算和提高精确度,并有助于设计、指导和分析实验。
Pluripotency factor binding and Tsix expression act synergistically to repress Xist in undifferentiated embryonic stem cells
Tatyana B Nesterova, Claire E Senner, Janina Schneider, Tilly Alcayna-Stevens, Anna Tattermusch, Myriam Hemberger, Neil Brockdorff
Epigenetics & Chromatin , 2011, DOI: 10.1186/1756-8935-4-17
Abstract: Here we employ a transgene strategy to test the role of the intron 1 element and Tsix in repressing Xist in ES cells. We find that deletion of the intron 1 element causes a small increase in Xist expression and that simultaneous deletion of the antisense regulator Tsix enhances this effect.We conclude that Tsix and pluripotency factors act synergistically to repress Xist in undifferentiated embryonic stem cells. Double mutants do not exhibit maximal levels of Xist expression, indicating that other pathways also play a role.In female mammals a developmentally regulated process, X inactivation, ensures silencing of a single X chromosome, balancing levels of X-linked genes relative to males [1]. X inactivation is mediated by the cis-acting non-coding RNA Xist that is transcribed from and coats the inactive X chromosome (Xi) elect [2]. Coating by Xist RNA triggers epigenetic modifications that silence transcription and establish a heritable heterochromatic state [3].X inactivation in the mouse occurs in two waves; imprinted X inactivation of the paternal X chromosome (Xp) that is initiated in two to four cell embryos and maintained in all cells until the blastocyst stage, and random X inactivation, initiated in the postimplantation epiblast. Embryo precursors in the inner cell mass (ICM) of the blastocyst reactivate Xp, reversing imprinted X inactivation and setting the ground state for the onset of random X inactivation [4,5]. XX embryonic stem (ES) cells, which are derived from the ICM, mirror this ground state, retaining two active X chromosomes [6,7]. In contrast extraembryonic trophectoderm and primitive endoderm lineages and cell lines derived thereof retain the imprinted X inactivation pattern through embryogenesis [8-11].X chromosome reactivation also occurs in XX primordial germ cells during migration towards the genital ridges [12-14], and similarly during experimental reprogramming of XX somatic cells, either by cloning, cell fusion with pluripotent cells or
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