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71.
72.
Several analytical and numerical eruption models have provided insight into volcanic eruption behaviour, but most address plinian-type eruptions where vent conditions are quasi-steady. Only a few studies have explored the physics of short-duration vulcanian explosions with unsteady vent conditions and blast events. Here we present a technique that links unsteady vent flux of vulcanian explosions to the resulting dispersal of volcanic ejecta, using a numerical, axisymmetric model with multiple particle sizes. We use observational data from well documented explosions in 1997 at the Soufrière Hills volcano in Montserrat, West Indies, to constrain pre-eruptive subsurface initial conditions and to compare with our simulation results. The resulting simulations duplicate many features of the observed explosions, showing transitional behaviour where mass is divided between a buoyant plume and hazardous radial pyroclastic currents fed by a collapsing fountain. We find that leakage of volcanic gas from the conduit through surrounding rocks over a short period (of the order of 10 hours) or retarded exsolution can dictate the style of explosion. Our simulations also reveal the internal plume dynamics and particle-size segregation mechanisms that may occur in such eruptions. 相似文献
73.
Energetic electrons and ions that are trapped in Earth's magnetosphere can suddenly be accelerated towards the planet. Some dynamic features of Earth's aurora (the northern and southern lights) are created by the fraction of these injected particles that travels along magnetic field lines and hits the upper atmosphere. Jupiter's aurora appears similar to Earth's in some respects; both appear as large ovals circling the poles and both show transient events. But the magnetospheres of Jupiter and Earth are so different---particularly in the way they are powered---that it is not known whether the magnetospheric drivers of Earth's aurora also cause them on Jupiter. Here we show a direct relationship between Earth-like injections of electrons in Jupiter's magnetosphere and a transient auroral feature in Jupiter's polar region. This relationship is remarkably similar to what happens at Earth, and therefore suggests that despite the large differences between planetary magnetospheres, some processes that generate aurorae are the same throughout the Solar System. 相似文献
74.
Berger E Ball S Becker KM Clarke M Frail DA Fukuda TA Hoffman IM Mellon R Momjian E Murphy NW Teng SH Woodruff T Zauderer BA Zavala RT 《Nature》2001,410(6826):338-340
Brown dwarfs are not massive enough to sustain thermonuclear fusion of hydrogen at their centres, but are distinguished from gas-giant planets by their ability to burn deuterium. Brown dwarfs older than approximately 10 Myr are expected to possess short-lived magnetic fields and to emit radio and X-rays only very weakly from their coronae. An X-ray flare was recently detected on the brown dwarf LP944-20, whereas previous searches for optical activity (and one X-ray search) yielded negative results. Here we report the discovery of quiescent and flaring radio emission from LP944-20, with luminosities several orders of magnitude larger than predicted by the empirical relation between the X-ray and radio luminosities that has been found for many types of stars. Interpreting the radio data within the context of synchrotron emission, we show that LP944-20 has an unusually weak magnetic field in comparison to active M-dwarf stars, which might explain the previous null optical and X-ray results, as well as the strength of the radio emissions compared to those at X-ray wavelengths. 相似文献
75.
Pryor WR Rymer AM Mitchell DG Hill TW Young DT Saur J Jones GH Jacobsen S Cowley SW Mauk BH Coates AJ Gustin J Grodent D Gérard JC Lamy L Nichols JD Krimigis SM Esposito LW Dougherty MK Jouchoux AJ Stewart AI McClintock WE Holsclaw GM Ajello JM Colwell JE Hendrix AR Crary FJ Clarke JT Zhou X 《Nature》2011,472(7343):331-333
Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity. 相似文献
76.
Ruslan?I.?DmitrievEmail author Sergey?M.?Borisov Alina?V.?Kondrashina Janelle?M.?P.?Pakan Ujval?Anilkumar Jochen?H.?M.?Prehn Alexander?V.?Zhdanov Kieran?W.?McDermott Ingo?Klimant Dmitri?B.?Papkovsky 《Cellular and molecular life sciences : CMLS》2015,72(2):367-381
Cell-permeable phosphorescent probes enable the study of cell and tissue oxygenation, bioenergetics, metabolism, and pathological states such as stroke and hypoxia. A number of such probes have been described in recent years, the majority consisting of cationic small molecule and nanoparticle structures. While these probes continue to advance, adequate staining for the study of certain cell types using live imaging techniques remains elusive; this is particularly true for neural cells. Here we introduce novel probes for the analysis of neural cells and tissues: negatively charged poly(methyl methacrylate-co-methacrylic acid)-based nanoparticles impregnated with a phosphorescent Pt(II)-tetrakis(pentafluorophenyl)porphyrin (PtPFPP) dye (this form is referred to as PA1), and with an additional reference/antennae dye poly(9,9-diheptylfluorene-alt-9,9-di-p-tolyl-9H-fluorene) (this form is referred to as PA2). PA1 and PA2 are internalised by endocytosis, result in efficient staining in primary neurons, astrocytes, and PC12 cells and multi-cellular aggregates, and allow for the monitoring of local O2 levels on a time-resolved fluorescence plate reader and PLIM microscope. PA2 also efficiently stains rat brain slices and permits detailed O2 imaging experiments using both one and two-photon intensity-based modes and PLIM modes. Multiplexed analysis of embryonic rat brain slices reveals age-dependent staining patterns for PA2 and a highly heterogeneous distribution of O2 in tissues, which we relate to the localisation of specific progenitor cell populations. Overall, these anionic probes are useful for sensing O2 levels in various cells and tissues, particularly in neural cells, and facilitate high-resolution imaging of O2 in 3D tissue models. 相似文献
77.
S. Padilla U. C. Tran M. Jiménez-Hidalgo J. M. López-Martín A. Martín-Montalvo C. F. Clarke P. Navas C. Santos-Ocaña 《Cellular and molecular life sciences : CMLS》2009,66(1):173-186
Coenzyme Q is a lipid molecule required for respiration and antioxidant protection. Q biosynthesis in Saccharomyces cerevisiae requires nine proteins (Coq1p–Coq9p). We demonstrate in this study that Q levels are modulated during growth by its conversion
from demethoxy-Q (DMQ), a late intermediate. Similar conversion was produced when cells were subjected to oxidative stress
conditions. Changes in Q6/DMQ6 ratio were accompanied by changes in COQ7 gene mRNA levels encoding the protein responsible for the DMQ hydroxylation, the penultimate step in Q biosynthesis pathway.
Yeast coq null mutant failed to accumulate any Q late biosynthetic intermediate. However, in coq7 mutants the addition of exogenous Q produces the DMQ synthesis. Similar effect was produced by over-expressing ABC1/COQ8. These results support the existence of a biosynthetic complex that allows the DMQ6 accumulation and suggest that Coq7p is a control point for the Q biosynthesis regulation in yeast.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Received 04 September 2008; received after revision 22 October 2008; accepted 23 October 2008 相似文献
78.
Multiplication of the scrapie agent 总被引:5,自引:0,他引:5
79.
Rapid eye movements and remembering 总被引:6,自引:0,他引:6
80.
C. H. Clarke 《Cellular and molecular life sciences : CMLS》1964,20(2):83-83
Résumé L'auteur décrit quatre souches deKlebsiella pneumoniae du type capsulaire B lysogènes pour les bactériophages actifs pour une autre souche du même type.
I am grateful to ProfessorsD. G. Catcheside andJ. P. Duguid, Drs.B. H. Park, I. Ørskov, J. Papavassiliou andY. Hamon for encouragement, information and bacterial strains. This work was begun at the Microbiology Department, University of Birmingham, while the author held an award from the Agricultural Research Council. 相似文献
I am grateful to ProfessorsD. G. Catcheside andJ. P. Duguid, Drs.B. H. Park, I. Ørskov, J. Papavassiliou andY. Hamon for encouragement, information and bacterial strains. This work was begun at the Microbiology Department, University of Birmingham, while the author held an award from the Agricultural Research Council. 相似文献