The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Alexander Heger - One of the best experts on this subject based on the ideXlab platform.
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large scale mixing in a violent oxygen Neon shell merger prior to a core collapse supernova
The Astrophysical Journal, 2020Co-Authors: Naveen Yadav, Bernhard Muller, H T Janka, Tobias Melson, Alexander HegerAbstract:We present a seven-minute long $4\pi$-3D simulation of a shell merger event in a non-rotating $18.88\, M_\odot$ supernova progenitor before the onset of gravitational collapse. The key motivation is to capture the large-scale mixing and asymmetries in the wake of the shell merger before collapse using a self-consistent approach. The $4\pi$ geometry is crucial as it allows us to follow the growth and evolution of convective modes on the largest possible scales. We find significant differences between the kinematic, thermodynamic and chemical evolution of the 3D and the 1D model. The 3D model shows vigorous convection leading to more efficient mixing of nuclear species. In the 3D case the entire oxygen shell attains convective Mach numbers of $\mathord{\approx}\, 0.1$, whereas in the 1D model, the convective velocities are much lower and there is negligible overshooting across convective boundaries. In the 3D case, the convective eddies entrain nuclear species from the Neon (and carbon) layers into the deeper part of the oxygen burning shell, where they burn and power a violent convection phase with outflows. This is a prototypical model of a convective-reactive system. Due to the strong convection and the resulting efficient mixing, the interface between the Neon layer and the silicon-enriched oxygen layer disappears during the evolution, and silicon is mixed far out into merged oxygen/Neon shell. Neon entrained inwards by convective downdrafts burns, resulting in lower Neon mass in the 3D model compared to the 1D model at time of collapse. In addition, the 3D model develops remarkable large-scale, large-amplitude asymmetries, which may have important implications for the impending gravitational collapse and the subsequent explosion.
Peter Bochsler - One of the best experts on this subject based on the ideXlab platform.
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estimation of the Neon oxygen abundance ratio at the heliospheric termination shock and in the local interstellar medium from ibex observations
Astrophysical Journal Supplement Series, 2012Co-Authors: Peter Bochsler, Eberhard Möbius, S. A. Fuselier, D. J. Mccomas, L Petersen, N A Schwadron, P Wurz, J A ScheerAbstract:We report the first direct measurement of the Ne/O abundance ratio of the interstellar neutral gas flowing into the inner heliosphere. From the first year of Interstellar Boundary Explorer IBEX data collected in spring 2009, we derive the fluxes of interstellar neutral oxygen and Neon. Using the flux ratio at the location of IBEX at 1 AU at the time of the observations, and using the ionization rates of Neon and oxygen prevailing in the heliosphere during the period of solar minimum, we estimate the Neon/oxygen ratios at the heliospheric termination shock and in the gas phase of the inflowing local interstellar medium. Our estimate is (Ne/O){sub gas,ISM} = 0.27 {+-} 0.10, which is-within the large given uncertainties-consistent with earlier measurements from pickup ions. Our value is larger than the solar abundance ratio, possibly indicating that a significant fraction of oxygen in the local interstellar medium is hidden in grains and/or ices.
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solar abundances of oxygen and Neon derived from solar wind observations
Astronomy and Astrophysics, 2007Co-Authors: Peter BochslerAbstract:Context. Recently, a revision of the solar abundances of C, N, and O to substantially lower values has led to a controversy on solar opacities in the solar standard model and to the suggestion to revise the solar abundance of Neon upward by as much as a factor of 1.6 leading to enhanced solar Neon/oxygen abundance ratios by a factor of 3. Neon and oxygen are neighboring elements with easily defined charged states in the solar wind, and they have been well identified and measured for over two decades in the solar wind under many circumstances and with several instruments. The solar wind Ne/O ratio is 0.14 with a conservative error estimate of ±0.03, consistent with the coronal value derived from solar energetic particle measurements. Aims. We investigate, whether solar wind observations are consistent with the newly proposed elemental solar abundances of Neon and oxygen. Methods. The solar helium abundance has been derived from helioseismological observations. Helium and Neon abundances in the solar wind have been well determined with the Apollo Foil experiments and, more recently, confirmed with the Genesis sample return mission. With these observations and the Neon/oxygen solar wind abundance ratio determined by in-situ mass-spectrometry and using a simple theoretical model of Coulomb-drag fractionation for the solar wind, we estimate solar abundances for Neon and oxygen. Results. From the variability of the helium/oxygen and the helium/Neon ratio in the solar wind and from theoretical considerations, we conclude that the helium/Neon ratio in the outer solar convective zone is 900 ± 110. Our best estimates of the solar Neon and oxygen abundances in logarithmic dex-units are [Ne] = 7.96 ± 0.13, and [O] = 8.87 ± 0.11. Conclusions. Our solar Neon/oxygen abundance ratio is consistent with the ratio derived from EUV-spectra from SOHO/CDS. However, our absolute abundance for oxygen is only marginally compatible with the newly derived value for oxygen, and our Neon value is clearly incompatible with the recently proposed enhancement of the solar Neon abundance.
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solar wind Neon from genesis implications for the lunar noble gas record
Science, 2006Co-Authors: A Grimberg, Peter Bochsler, H Baur, F Buhler, D S Burnett, Charles C Hays, V S Heber, A J G Jurewicz, R WielerAbstract:Lunar soils have been thought to contain two solar noble gas components with distinct isotopic composition. One has been identified as implanted solar wind, the other as higher-energy solar particles. The latter was puzzling because its relative amounts were much too large compared with present-day fluxes, suggesting periodic, very high solar activity in the past. Here we show that the depth-dependent isotopic composition of Neon in a metallic glass exposed on NASA's Genesis mission agrees with the expected depth profile for solar wind Neon with uniform isotopic composition. Our results strongly indicate that no extra high-energy component is required and that the solar Neon isotope composition of lunar samples can be explained as implantation-fractionated solar wind.
Kenneth S. Suslick - One of the best experts on this subject based on the ideXlab platform.
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non boltzmann population distributions during single bubble sonoluminescence
Journal of Physical Chemistry B, 2013Co-Authors: David J. Flannigan, Kenneth S. SuslickAbstract:Single-bubble sonoluminescence (SBSL) spectra from aqueous sulfuric acid solutions containing dissolved Neon show widely varying emission despite being similar in chemical composition. From a 65 wt % solution, emission from hydroxyl radicals is observed, with the rovibronic progression being well-described by a single temperature of 7600 K. From an 80 wt % solution, however, emission spectra reveal vibrationally hot sulfur monoxide (SO; Tv = 2400 K) that is also rotationally cold (Tr = 280 K). Further, the SO vibrational population distribution is best-described by a non-Boltzmann distribution. Excited Neon atom emission observed from the 80 wt % solution gives an estimated temperature of only 3400 K, indicative of emission from a cool outer shell at the interfacial region. The Neon atom excited-state population is also best-described by a non-Boltzmann distribution. These observations are consistent with SBSL emission having both a spatial and temporal component, and the implications for these effects are discussed.
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temperature nonequilibration during single bubble sonoluminescence
Journal of Physical Chemistry Letters, 2012Co-Authors: David J. Flannigan, Kenneth S. SuslickAbstract:Single-bubble sonoluminescence (SBSL) spectra from liquids having low vapor pressures, especially mineral acids, are exceptionally rich. During SBSL from aqueous sulfuric acid containing dissolved Neon, rovibronic emission spectra reveal vibrationally hot sulfur monoxide (SO; Tv = 2100 K) that is also rotationally cold (Tr = 290 K). In addition to SO, excited Neon atom emission gives an estimated temperature, for Neon, of several thousand Kelvin. This nonequilibrated temperature is consistent with dynamically constrained SO formation at the liquid-vapor interface of the collapsing bubble. Formation occurs via collisions of fast Neon atoms (generated within the collapsing bubble) with liquid-phase molecular species in the interfacial region, thus allowing for a mechanistic understanding of the processes leading to light emission.
Martin A Gorovsky - One of the best experts on this subject based on the ideXlab platform.
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a robust inducible repressible promoter greatly facilitates gene knockouts conditional expression and overexpression of homologous and heterologous genes in tetrahymena thermophila
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Yuhua Shang, Xiaoyuan Song, Josephine Bowen, Robert Corstanje, Yan Gao, Jacek Gaertig, Martin A GorovskyAbstract:The Cd(2+)-inducible metallothionein (MTT1) gene was cloned from Tetrahymena thermophila. Northern blot analysis showed that MTT1 mRNA is not detectable in the absence of Cd(2+), is induced within 10 min of its addition, is expressed in proportion to its concentration, and rapidly disappears upon its withdrawal. Similarly, when the neo1 gene coding region flanked by the MTT1 gene noncoding sequences was used to disrupt the MTT1 locus, no transformants were observed in the absence of Cd(2+), and the number of transformants was proportional to increased Cd(2+) concentration. The neo3 cassette, in which the MTT1 promoter replaced the histone gene HHF1 promoter of the previously used neo2 cassette, transformed cells at much higher frequencies than neo2 and produced germ-line knockouts where neo2 had failed. Rescuing the progeny of a mating of gamma-tubulin gene, GTU1, knockout heterokaryons with a GTU1 gene inserted into the MTT1 locus yielded >75 times more transformants than rescuing with the wild-type GTU1 gene itself. When cells rescued with the MTT1-GTU1 chimeric gene were transferred to medium lacking Cd(2+), they stopped growing and had phenotypic changes indistinguishable from cells containing only disrupted GTU1 genes. Thus, it is now possible to create conditional lethal mutants and study the terminal phenotypes of null mutations for essential genes by replacing the endogenous gene with one under the control of the MTT1 promoter. The MTT1 promoter also resulted in approximately 30 times more overexpression of the IAG48[G1] surface antigen gene of the ciliate fish parasite Ichthyophthirius multifiliis than the highly expressed BTU1 promoter, accounting for approximately 1% of the total cell protein. Thus, the MTT1 promoter should enable routine over-expression of endogenous and foreign genes in Tetrahymena.
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a robust inducible repressible promoter greatly facilitates gene knockouts conditional expression and overexpression of homologous and heterologous genes in tetrahymena thermophila
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Yuhua Shang, Xiaoyuan Song, Josephine Bowen, Robert Corstanje, Jacek Gaertig, Martin A GorovskyAbstract:The Cd2+-inducible metallothionein (MTT1) gene was cloned from Tetrahymena thermophila. Northern blot analysis showed that MTT1 mRNA is not detectable in the absence of Cd2+, is induced within 10 min of its addition, is expressed in proportion to its concentration, and rapidly disappears upon its withdrawal. Similarly, when the neo1 gene coding region flanked by the MTT1 gene noncoding sequences was used to disrupt the MTT1 locus, no transformants were observed in the absence of Cd2+, and the number of transformants was proportional to increased Cd2+ concentration. The neo3 cassette, in which the MTT1 promoter replaced the histone gene HHF1 promoter of the previously used neo2 cassette, transformed cells at much higher frequencies than neo2 and produced germ-line knockouts where neo2 had failed. Rescuing the progeny of a mating of γ-tubulin gene, GTU1, knockout heterokaryons with a GTU1 gene inserted into the MTT1 locus yielded >75 times more transformants than rescuing with the wild-type GTU1 gene itself. When cells rescued with the MTT1-GTU1 chimeric gene were transferred to medium lacking Cd2+, they stopped growing and had phenotypic changes indistinguishable from cells containing only disrupted GTU1 genes. Thus, it is now possible to create conditional lethal mutants and study the terminal phenotypes of null mutations for essential genes by replacing the endogenous gene with one under the control of the MTT1 promoter. The MTT1 promoter also resulted in ≈30 times more overexpression of the IAG48[G1] surface antigen gene of the ciliate fish parasite Ichthyophthirius multifiliis than the highly expressed BTU1 promoter, accounting for ≈1% of the total cell protein. Thus, the MTT1 promoter should enable routine over-expression of endogenous and foreign genes in Tetrahymena.
Bernhard Muller - One of the best experts on this subject based on the ideXlab platform.
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large scale mixing in a violent oxygen Neon shell merger prior to a core collapse supernova
The Astrophysical Journal, 2020Co-Authors: Naveen Yadav, Bernhard Muller, H T Janka, Tobias Melson, Alexander HegerAbstract:We present a seven-minute long $4\pi$-3D simulation of a shell merger event in a non-rotating $18.88\, M_\odot$ supernova progenitor before the onset of gravitational collapse. The key motivation is to capture the large-scale mixing and asymmetries in the wake of the shell merger before collapse using a self-consistent approach. The $4\pi$ geometry is crucial as it allows us to follow the growth and evolution of convective modes on the largest possible scales. We find significant differences between the kinematic, thermodynamic and chemical evolution of the 3D and the 1D model. The 3D model shows vigorous convection leading to more efficient mixing of nuclear species. In the 3D case the entire oxygen shell attains convective Mach numbers of $\mathord{\approx}\, 0.1$, whereas in the 1D model, the convective velocities are much lower and there is negligible overshooting across convective boundaries. In the 3D case, the convective eddies entrain nuclear species from the Neon (and carbon) layers into the deeper part of the oxygen burning shell, where they burn and power a violent convection phase with outflows. This is a prototypical model of a convective-reactive system. Due to the strong convection and the resulting efficient mixing, the interface between the Neon layer and the silicon-enriched oxygen layer disappears during the evolution, and silicon is mixed far out into merged oxygen/Neon shell. Neon entrained inwards by convective downdrafts burns, resulting in lower Neon mass in the 3D model compared to the 1D model at time of collapse. In addition, the 3D model develops remarkable large-scale, large-amplitude asymmetries, which may have important implications for the impending gravitational collapse and the subsequent explosion.
