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Annuar A, Gandhi P, Alexander DM, Lansbury GB, Arévalo P, Ballantyne DR, Baloković M, Bauer FE, Boggs SE, Brandt WN, Brightman M, Christensen FE, Craig WW, Moro AD, Hailey CJ, Harrison FA, Hickox RC, Matt G, Puccetti S, Ricci C, Rigby JR, Stern D, Walton DJ, Zappacosta L, Zhang W. NuSTAROBSERVATIONS OF THE COMPTON-THICK ACTIVE GALACTIC NUCLEUS AND ULTRALUMINOUS X-RAY SOURCE CANDIDATE IN NGC 5643. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0004-637x/815/1/36] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Teng SH, Rigby JR, Stern D, Ptak A, Alexander DM, Bauer FE, Boggs SE, Brandt WN, Christensen FE, Comastri A, Craig WW, Farrah D, Gandhi P, Hailey CJ, Harrison FA, Hickox RC, Koss M, Luo B, Treister E, Zhang WW. ANuSTARSURVEY OF NEARBY ULTRALUMINOUS INFRARED GALAXIES. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0004-637x/814/1/56] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Boggs SE, Harrison FA, Miyasaka H, Grefenstette BW, Zoglauer A, Fryer CL, Reynolds SP, Alexander DM, An H, Barret D, Christensen FE, Craig WW, Forster K, Giommi P, Hailey CJ, Hornstrup A, Kitaguchi T, Koglin JE, Madsen KK, Mao PH, Mori K, Perri M, Pivovaroff MJ, Puccetti S, Rana V, Stern D, Westergaard NJ, Zhang WW. 44
Ti gamma-ray emission lines from SN1987A reveal an asymmetric explosion. Science 2015; 348:670-1. [DOI: 10.1126/science.aaa2259] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- S. E. Boggs
- Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
| | - F. A. Harrison
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - H. Miyasaka
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - B. W. Grefenstette
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - A. Zoglauer
- Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
| | - C. L. Fryer
- CCS-2, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - S. P. Reynolds
- Physics Department, NC State University, Raleigh, NC 27695, USA
| | - D. M. Alexander
- Department of Physics, Durham University, Durham DH1 3LE, UK
| | - H. An
- Department of Physics, McGill University, Rutherford Physics Building, Montreal, Quebec H3A 2T8, Canada
| | - D. Barret
- Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
- CNRS, Institut de Recherche en Astrophysique et Planétologie, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France
| | - F. E. Christensen
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
| | - W. W. Craig
- Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - K. Forster
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - P. Giommi
- Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc I-00133, Roma, Italy
| | - C. J. Hailey
- Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
| | - A. Hornstrup
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
| | - T. Kitaguchi
- RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - J. E. Koglin
- Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - K. K. Madsen
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - P. H. Mao
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - K. Mori
- Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA
| | - M. Perri
- Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc I-00133, Roma, Italy
- INAF – Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio, Italy
| | - M. J. Pivovaroff
- Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - S. Puccetti
- Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc I-00133, Roma, Italy
- INAF – Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio, Italy
| | - V. Rana
- Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
| | - D. Stern
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - N. J. Westergaard
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
| | - W. W. Zhang
- NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
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Baloković M, Comastri A, Harrison FA, Alexander DM, Ballantyne DR, Bauer FE, Boggs SE, Brandt WN, Brightman M, Christensen FE, Craig WW, Moro AD, Gandhi P, Hailey CJ, Koss M, Lansbury GB, Luo B, Madejski GM, Marinucci A, Matt G, Markwardt CB, Puccetti S, Reynolds CS, Risaliti G, Rivers E, Stern D, Walton DJ, Zhang WW. THENuSTARVIEW OF NEARBY COMPTON-THICK ACTIVE GALACTIC NUCLEI: THE CASES OF NGC 424, NGC 1320, AND IC 2560. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/0004-637x/794/2/111] [Citation(s) in RCA: 85] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Luo B, Brandt WN, Alexander DM, Stern D, Teng SH, Arévalo P, Bauer FE, Boggs SE, Christensen FE, Comastri A, Craig WW, Farrah D, Gandhi P, Hailey CJ, Harrison FA, Koss M, Ogle P, Puccetti S, Saez C, Scott AE, Walton DJ, Zhang WW. WEAK HARD X-RAY EMISSION FROM BROAD ABSORPTION LINE QUASARS: EVIDENCE FOR INTRINSIC X-RAY WEAKNESS. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/0004-637x/794/1/70] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Grefenstette BW, Harrison FA, Boggs SE, Reynolds SP, Fryer CL, Madsen KK, Wik DR, Zoglauer A, Ellinger CI, Alexander DM, An H, Barret D, Christensen FE, Craig WW, Forster K, Giommi P, Hailey CJ, Hornstrup A, Kaspi VM, Kitaguchi T, Koglin JE, Mao PH, Miyasaka H, Mori K, Perri M, Pivovaroff MJ, Puccetti S, Rana V, Stern D, Westergaard NJ, Zhang WW. Asymmetries in core-collapse supernovae from maps of radioactive 44Ti in Cassiopeia A. Nature 2014; 506:339-42. [PMID: 24553239 DOI: 10.1038/nature12997] [Citation(s) in RCA: 180] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2013] [Accepted: 12/13/2013] [Indexed: 11/09/2022]
Abstract
Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive (44)Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. Cassiopeia A is a young, nearby, core-collapse remnant from which (44)Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed (44)Ti emission to estimated (56)Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the (44)Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the (44)Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.
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Affiliation(s)
- B W Grefenstette
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - F A Harrison
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - S E Boggs
- Space Sciences Laboratory, University of California, Berkeley, California 94720, USA
| | - S P Reynolds
- Physics Department, North Carolina State University, Raleigh, North Carolina 27695, USA
| | - C L Fryer
- CCS-2, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - K K Madsen
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - D R Wik
- NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
| | - A Zoglauer
- Space Sciences Laboratory, University of California, Berkeley, California 94720, USA
| | - C I Ellinger
- Department of Physics, University of Texas at Arlington, Arlington, Texas 76019, USA
| | - D M Alexander
- Department of Physics, Durham University, Durham DH1 3LE, UK
| | - H An
- Department of Physics, McGill University, Rutherford Physics Building, Montreal, Quebec H3A 2T8, Canada
| | - D Barret
- 1] Université de Toulouse, UPS-OMP, IRAP, 9 Avenue du Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France [2] CNRS, Institut de Recherche en Astrophysique et Planétologie, 9 Avenue colonel Roche, BP 44346, F-31028 Toulouse Cedex 4, France
| | - F E Christensen
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
| | - W W Craig
- 1] Space Sciences Laboratory, University of California, Berkeley, California 94720, USA [2] Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - K Forster
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - P Giommi
- Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc, I-00133 Roma, Italy
| | - C J Hailey
- Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA
| | - A Hornstrup
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
| | - V M Kaspi
- Department of Physics, McGill University, Rutherford Physics Building, Montreal, Quebec H3A 2T8, Canada
| | - T Kitaguchi
- RIKEN, Nishina Center, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan
| | - J E Koglin
- Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
| | - P H Mao
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - H Miyasaka
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - K Mori
- Columbia Astrophysics Laboratory, Columbia University, New York, New York 10027, USA
| | - M Perri
- 1] Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc, I-00133 Roma, Italy [2] INAF - Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio, Italy
| | - M J Pivovaroff
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - S Puccetti
- 1] Agenzia Spaziale Italiana (ASI) Science Data Center, Via del Politecnico snc, I-00133 Roma, Italy [2] INAF - Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio, Italy
| | - V Rana
- Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, California 91125, USA
| | - D Stern
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
| | - N J Westergaard
- DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
| | - W W Zhang
- NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
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Abstract
A viroid has been purified from avocado leaves infected by sunblotch disease and designated the avocado sunblotch viroid. It is a covalently closed circular RNA molecule with a molecular weight lower than that of chrysanthemum stunt viroid and citrus exocortis viroid while hybridization analysis with 32P-labeled complementary DNA indicated that it is a single RNA species. It could be detected as a stainable RNA band on polyacrylamide tube gel electrophoresis of partially purified extracts of only two of four avocado isolates with positive symptoms of sunblotch disease. However, the viroid was detected in all four isolates by hybridization analysis with 32P-complementary DNA; this procedure has potential use for the rapid indexing of sunblotch disease since the viroid was not present in an isolate of healthy avocado. It has yet to be shown that the viroid is the causative agent of sunblotch disease.
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Affiliation(s)
- P Palukaitis
- Department of Biochemistry, University of Adelaide, Adelaide 5001, South Australia
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Alexander DM, Williams LM, Gatt JM, Dobson-Stone C, Kuan SA, Todd EG, Schofield PR, Cooper NJ, Gordon E. The contribution of apolipoprotein E alleles on cognitive performance and dynamic neural activity over six decades. Biol Psychol 2007; 75:229-38. [PMID: 17433528 DOI: 10.1016/j.biopsycho.2007.03.001] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2006] [Revised: 03/08/2007] [Accepted: 03/08/2007] [Indexed: 10/23/2022]
Abstract
Neuroimaging shows brain-functional differences due to apolipoprotein E (APOE) polymorphisms may exist decades before the increased risk period for Alzheimer's disease, but little is known about their effect on cognition and brain function in children and young adults. This study assessed 415 healthy epsilon2 and epsilon4 carriers and matched epsilon3/epsilon3 controls, spanning ages 6-65, on a range of cognitive tests. Subjects were also compared on a new dynamical measure of EEG activity during a visual working memory task using alphabetical stimuli. epsilon4 subjects had better verbal fluency compared to epsilon3, an effect that was strongest in 51-65 year-olds. No epsilon4 deficits in cognition were found. In 6-15 year-olds, there were differences in total spatio-temporal wave activity between epsilon3 and epsilon4 subjects in the theta band, approximately 200ms post-stimulus. Differences in brain function in younger epsilon4 subjects and superior verbal fluency across the entire age range suggest that the APOE epsilon4 allele is an example of antagonistic pleiotropy.
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Affiliation(s)
- D M Alexander
- Brain Resource Company and Brain Resource International Database, PO Box 737, Broadway, NSW 2007, Australia.
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11
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Alexander DM, Wright JJ. The maximum range and timing of excitatory contextual modulation in monkey primary visual cortex. Vis Neurosci 2006; 23:721-8. [PMID: 17020628 DOI: 10.1017/s0952523806230049] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2004] [Accepted: 03/27/2006] [Indexed: 11/06/2022]
Abstract
Contextual modulations of receptive field properties by distal stimulus configurations have been shown for a variety of stimulus paradigms. A survey of excitatory contextual modulation data for V1 shows the maximum scale of interactions, measured in terms of distance in V1, to be between 10 mm and 30 mm. Different types of excitatory contextual modulation in V1 occur throughout the interval of 40-250 ms after stimulus delivery. This window provides opportunity for global propagation of visual contextual information to a subset of V1 neurons, via several routes within the visual system. We propose a number of experiments and analyses to confirm the results from this empirical survey.
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Affiliation(s)
- D M Alexander
- Faculty of Information Technology, University of Technology, Sydney, Australia.
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12
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Alexander DM, Trengove C, Wright JJ, Boord PR, Gordon E. Measurement of phase gradients in the EEG. J Neurosci Methods 2006; 156:111-28. [PMID: 16574240 DOI: 10.1016/j.jneumeth.2006.02.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2005] [Revised: 02/04/2006] [Accepted: 02/13/2006] [Indexed: 11/23/2022]
Abstract
Previous research has shown that spatio-temporal waves in the EEG are generally of long spatial wavelength and form smooth patterns of phase gradients at particular time-samples. This paper describes a method to measure smooth phase gradients of long spatial wavelength in the EEG. The method depends on the global pattern of phase at a given frequency and time and is therefore robust to variations, over time, in phase-lag between particular sites. Phases were estimated in the EEG signal using wavelet or short time-series Fourier methods. During an auditory oddball task, phases across the scalp tend to fall within a limited circular range, a range that is not indicative of phase-synchrony nor waves with multiple periods. At times the phases tended to maintain a spatially and temporally ordered relationship. The relative phases were analysed using three phase gradient basis functions, providing a measure of the amount of variance explained, across the electrodes, by smooth changes in relative phase from a single minimum or single maximum. The data from 586 adult subjects were analysed and it was found that the probability of phase gradient events varies with time and frequency in the stimulus-locked average, and with task demands. The temporal extent of spatio-temporal waves was measured by detecting smoothly changing patterns of phase latencies across the scalp. The specific spatial pattern and timing of phase gradients correspond closely to the latency distributions of certain ERPs.
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Affiliation(s)
- D M Alexander
- Brain Resource Company and Brain Resource International Database, PO Box 737, Broadway, Sydney, 2007 NSW, Australia.
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Wright JJ, Alexander DM, Bourke PD. Contribution of lateral interactions in V1 to organization of response properties. Vision Res 2006; 46:2703-20. [PMID: 16600322 DOI: 10.1016/j.visres.2006.02.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2005] [Revised: 12/04/2005] [Accepted: 02/14/2006] [Indexed: 11/30/2022]
Abstract
We propose a model of self-organization of synaptic connections in V1, emphasizing lateral interactions. Subject to Hebbian learning with decay, evolution of synaptic strengths proceeds to a stable state in which all synapses are either saturated, or have minimum pre/post-synaptic coincidence. The most stable configuration gives rise to anatomically realistic "local maps", each of macro-columnar size, and each organized as Mobius projections of retinotopic space. A tiling of V1, constructed of approximately mirror-image reflections of each local map by its neighbors is formed, accounting for orientation-preference singularities, linear zones, and saddle points-with each map linked by connections between sites of common orientation preference. Ocular dominance columns are partly explained as a special case of the same process. The occurrence of direction preference fractures always in odd numbers around singularities is a specific feature explained by the Mobius configuration of the local map. Effects of stimulus velocity, orientation relative to direction of motion, and extension, upon orientation preference, which are not accounted for by spatial filtering, are explained by interactions between the classic receptive field and global V1.
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Affiliation(s)
- J J Wright
- Liggins Institute, University of Auckland, Auckland, New Zealand.
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Alexander DM, Smail I, Bauer FE, Chapman SC, Blain AW, Brandt WN, Ivison RJ. Rapid growth of black holes in massive star-forming galaxies. Nature 2005; 434:738-40. [PMID: 15815623 DOI: 10.1038/nature03473] [Citation(s) in RCA: 184] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2004] [Accepted: 02/11/2005] [Indexed: 11/09/2022]
Abstract
The tight relationship between the masses of black holes and galaxy spheroids in nearby galaxies implies a causal connection between the growth of these two components. Optically luminous quasars host the most prodigious accreting black holes in the Universe, and can account for greater than or approximately equal to 30 per cent of the total cosmological black-hole growth. As typical quasars are not, however, undergoing intense star formation and already host massive black holes (> 10(8)M(o), where M(o) is the solar mass), there must have been an earlier pre-quasar phase when these black holes grew (mass range approximately (10(6)-10(8))M(o)). The likely signature of this earlier stage is simultaneous black-hole growth and star formation in distant (redshift z > 1; >8 billion light years away) luminous galaxies. Here we report ultra-deep X-ray observations of distant star-forming galaxies that are bright at submillimetre wavelengths. We find that the black holes in these galaxies are growing almost continuously throughout periods of intense star formation. This activity appears to be more tightly associated with these galaxies than any other coeval galaxy populations. We show that the black-hole growth from these galaxies is consistent with that expected for the pre-quasar phase.
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Affiliation(s)
- D M Alexander
- Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK.
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15
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Alexander DM, Trengove C, Johnston P, Cooper T, August JP, Gordon E. Separating individual skin conductance responses in a short interstimulus-interval paradigm. J Neurosci Methods 2005; 146:116-23. [PMID: 15935228 DOI: 10.1016/j.jneumeth.2005.02.001] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2004] [Revised: 01/27/2005] [Accepted: 02/01/2005] [Indexed: 11/30/2022]
Abstract
We describe a new method for measuring skin conductance responses, designed to overcome the problem of overlapping skin conductance responses. The method relies on the assumptions that the underlying sudomotor nerve signal has a shorter time-constant than the skin conductance signal itself, and that the sudomotor bursts arrive as discrete, separated events. By converting the skin conductance signal into a time-series with a shorter time-constant, we are able to extract the separated peaks in the estimated underlying driver signal. The separated driver peaks are then used to re-estimate each individual skin conductance response. The method is automated and applied to a normative database of 735 subjects, for which skin conductance was measured during an auditory oddball paradigm.
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Affiliation(s)
- D M Alexander
- Brain Resource Company, PO Box 737, Broadway, Sydney, 2007 NSW, Australia.
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Liley DT, Alexander DM, Wright JJ, Aldous MD. Alpha rhythm emerges from large-scale networks of realistically coupled multicompartmental model cortical neurons. Network 1999; 10:79-92. [PMID: 10372763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Conical pyramidal and stellate neurons were simulated using the GENESIS simulation package. Model neurons were leaky integrate-and-fire and consisted of from four to nine passive compartments. Neurophysiological measurements, based on single-cell recordings and patch-clamp experiments, provided estimations for the simulation of cortical neurons: transmitter-activated conductances, passive membrane time constants and axonal delays. Network connectivity was generated using a previously described probabilistic scheme based on known cortical histology, in which the probability of connections forming between one neuron and another fell off monotonically with increasing inter-cellular separation. Simulations of up to 6400 cortical neurons, approaching the scale of an individual cortical column, confirmed previous findings with smaller networks. Limit-cycle behaviour emerged in the network, in the frequency in the range of the mammalian alpha and beta rhythms (8-20 Hz). Contrary to expectation, near-linear relationships were found between the mean soma membrane potential and and neuronal firing probability. Some of the implications for cortical information processing, in particular the dynamical interactions between the neuronal and larger scales, are discussed.
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Affiliation(s)
- D T Liley
- School of Biophysical Sciences and Electrical Engineering, Swinburne University of Technology, Hawthorn, Vic, Australia
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Alexander DM, St John AC. Characterization of the carbon starvation-inducible and stationary phase-inducible gene slp encoding an outer membrane lipoprotein in Escherichia coli. Mol Microbiol 1994; 11:1059-71. [PMID: 8022277 DOI: 10.1111/j.1365-2958.1994.tb00383.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Escherichia coli induces the expression of more than 50 proteins in response to starvation for a carbon source. Strains MC7 (csi7::phoA) and MC19 (csi19::phoA) contain fusions of a signal peptide-deficient phoA reporter sequence to a csi (carbon starvation-inducible) gene. PhoA expression increased when these strains were deprived of a carbon source or entered stationary phase but did not when the cells were deprived of a nitrogen source or subjected to osmotic, oxidative or thermal stress. Mapping and sequence analysis of the cloned phoA fusions in strains MC7 and MC19 indicated that they had occurred in different locations within the same previously unidentified gene. The wild-type allele of this gene was cloned and the encoded protein was found to be a new lipoprotein. Therefore we propose to call this locus slp (starvation lipoprotein). The 22 kDa Slp protein is associated with the outer membrane fraction. The slp gene was located at 78.6 centisomes on the E. coli genetic map. The -10 and -35 regions upstream of the mRNA start site were characteristic of a sigma 70 promoter. The major transcript from this promoter was sufficiently large to contain slp sequences but not the downstream open reading frame. Induction of beta-galactosidase activity from a slp::lacZ translational fusion during carbon starvation or stationary phase was independent of cAMP, RpoS (KatF) and DnaK, all of which are known to affect the expression of certain starvation-inducible or stationary phase-inducible proteins.
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Affiliation(s)
- D M Alexander
- Department of Biological Sciences, Rutgers, State University of New Jersey, Piscataway 08855-1059
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Alexander DM, Hesson T, Mannarino A, Cable M, Dalie BL. Isolation and purification of a biologically active human platelet-derived growth factor BB expressed in Escherichia coli. Protein Expr Purif 1992; 3:204-11. [PMID: 1392617 DOI: 10.1016/1046-5928(92)90016-p] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Human platelet-derived growth factor (PDGF) was expressed in Escherichia coli from a high-level cytoplasmic expression vector. A cDNA fragment encoding the mature form of the human PDGF B chain (hPDGF-B) was cloned into a plasmid under transcriptional control of the inducible E. coli Tac promoter. Expression of hPDGF-B from the final construct, pTacBIq, is regulated by the lactose repressor (LacIq). Upon induction, a polypeptide of approximately 14 kDa that had the same molecular mass and immunoreactivity as authentic hPDGF-B was produced. The production of recombinant hPDGF-B was significantly increased in an E. coli strain (CAG629) defective in expression of the lon protease. Expression of hPDGF-B in the CAG629 strain accounted for approximately 1% of total cell protein. In this system, hPDGF-B is expressed as an insoluble, intracellular protein and can readily be obtained in a partially purified form after differential centrifugation. Amino acid sequence determination of the purified protein has verified that the amino-terminal portion of the recombinant PDGF is correct. After renaturation into dimers, the purified recombinant hPDGF is fully functional in assays for receptor binding and mitogenesis.
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Affiliation(s)
- D M Alexander
- Department of Biotechnology/Molecular Biology, Schering-Plough Research, Bloomfield, New Jersey 07003
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Abstract
The particulate contamination in 12 formulations of antibiotic solutions in vials packed as dry powders from five South African sources has been analysed quantitatively using a HIAC PC 320 light blockage particle analyser linked to a CMB 60 sensor. Results showed that the level of particulate contamination fell well within the limits set by the USP XXIst Edition for Small Volume Parenterals although four formulations contained some particles greater than or equal to 50 micron. There was no apparent difference between the quality of the same antibiotics from different sources or between vials of the same antibiotics packed in different strengths.
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Affiliation(s)
- D M Alexander
- Department of Pharmacy, University of Durban-Westville, Republic of South Africa
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Abstract
The metabolism of phenylbutazone has been investigated in female rats dosed with the drug by gavage. The major route of excretion is via the urine; 50% of the dose being excreted in the first 24 h. A small percentage of the dose is excreted in the faeces. Following administration of 14C-phenylbutazone, five labelled, unconjugated hydroxy compounds were identified in the urine by t.l.c. and autoradiography; both hydrolysable and non-hydrolysable conjugates were found. Aqueous extracts of faeces contained O conjugates of oxyphenbutazone and 4-hydroxy-oxyphenbutazone (which may be a decomposition product). Urine metabolites soluble in organic solvents were quantified by inverse isotope dilution assay and spectrophotometric analysis. The major metabolite is the gamma-hydroxy derivative of phenylbutazone present both as the lactone and as the straight-chain compound, while oxyphenbutazone and p, gamma-dihydroxyphenylbutazone are minor metabolites.
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23
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Abstract
The particulate contamination in 19 formulations of solutions in ampoules supplied by eight South African manufacturers, thirty-three batches in all, was analysed using a HIAC PC 320 light blockage particle analyser linked to a CMB 60 sensor. Results showed that the level of contamination was generally low and that, where comparisons could be made, manufacturers both of the ampoules and the solutions maintained similarly high standards. Problems in this field appeared to be related to the formulation or the quality of the raw material.
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24
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Abstract
A method of opening ampoules without introducing particles has been developed and the level of particulate contamination in a number of ampoule solutions using a light blockage particle analyser (HIAC) has been determined. Low levels of contamination were found and a method of setting limits of particulate contamination in ampoules is suggested.
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25
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Abstract
Relative viscosities have
been measured of dilute aqueous solutions of aliphatic alcohols, including
methanol, ethanol, the propanols, the butanols and the pentanols, at
temperatures of 278, 293 and 313 K at concentrations in the range 10-4-10-2
mol dm-3. The Jones and Dole B
coefficients have been calculated and compared with literature data
extrapolated to low concentrations.
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26
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Abstract
A semiempirical equation is
proposed to describe the effect on the viscosity of a solvent due to the addition
of a solute. This equation is applied to many types of mixtures but not those
for which components are electrolytes or water. The B coefficient at infinite
dilution is B°2 = V·1
+ V·2 /2[ln��
η·2�/In η·1 -
H°/2-H·2
/ 2.45RT ]
where H°2-H·2
is the heat of solution of the liquid solute, V·1 and V·2
the molar volumes and η·2 and η·1
the viscosities of the pure components.
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27
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Abstract
An equation is presented
which represents the variation of viscosity of a liquid with pressure in terms
of the compressibility (βT), thermal
expansion (α) and molar volume (V) of the liquid (∂In
η/∂P)T = βT+(Vα/2.45R)
The derivation of the
equation from an equation developed by Eyring and
coworkers is given and the application of the equation is shown to 17 liquids
for which data are available.
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28
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Abstract
An equation is proposed to
describe the viscosity B coefficients
for dilute solutions of nonelectrolytes in water. It
is based on an empirical equation developed for nonaqueous
mixtures and an assumption that the entropy change on solution of the liquid solute
affects the viscosity of the aqueous system in the same way as a change of
molar entropy affects the viscosity of pure water. The equation is shown to
represent experimental results well and is especially successful in
representing the temperature dependence of the B coefficient for aqueous solutions of alcohols.
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29
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Abstract
Aqueous solubility
measurements for a number of non-electrolyte solutes have been analysed using a
statistical method of curve fitting to yield the best unbiased estimates of the
thermodynamic function changes on solution. The variation of partial molar heat
capacity changes with temperature has been discussed.
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30
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Abstract
A new calorimeter has been
developed and the enthalpy of solution of methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, and 2- methylpropan-2-ol,
in water to low concentrations, measured between 5� and 35�. In all cases, the
results can be adequately represented by a quadratic dependence of heat of
solution on temperature. The results have been compared qualitatively with the
data for the hydrocarbons.
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32
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Abstract
Apparent molar volumes of propan-2-ol have
been determined in dilute aqueous solution from 0� to 80�. Structural volume
changes in propan-1-ol and propan-2-ol solutions are discussed and related to compressibilities.
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