366 research outputs found

    A Spectacular Bow Shock in the 11 keV Galaxy Cluster Around 3C 438

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    This is a pre-copyedited, author-produced pdf of an article accepted for publication in The Astrophysical Journal following peer review. The version of record, Deanna L. Emery; Ákos BogdĂĄn; Ralph P. Kraft; Felipe Andrade-Santos; William R. Forman; Martin Hardcastle; and Christine Jones, ‘A spectacular bow shock in the 11 keV galaxy cluster around 3C 438’, The Astrophysical Journal (2017) 834(2):159 (7pp), published 10 January 2017, is available at doi: 10.3847/1538-4357/834/2/159 © 2017. The American Astronomical Society. All rights reserved.We present results of deep 153 ks Chandra observations of the hot, 11 keV, galaxy cluster associated with the radio galaxy 3C 438. By mapping the morphology of the hot gas and analyzing its surface brightness and temperature distributions, we demonstrate the presence of a merger bow shock. We identify the presence of two jumps in surface brightness and in density located at ∌\sim400 kpc and ∌\sim800 kpc from the cluster's core. At the position of the inner jump, we detect a factor of 2.3±0.22.3\pm 0.2 density jump, while at the location of the outer jump, we detect a density drop of a factor of 3.5±0.73.5 \pm 0.7. Combining this with the temperature distribution within the cluster, we establish that the pressure of the hot gas is continuous at the 400 kpc jump, while there is a factor of 6.2±2.86.2 \pm 2.8 pressure discontinuity at 800 kpc jump. From the magnitude of the outer pressure discontinuity, using the Rankine-Hugoniot jump conditions, we determine that the sub-cluster is moving at M=2.3±0.5M = 2.3\pm 0.5, or approximately 2600±5652600\pm 565 km/s through the surrounding intracluster medium, creating the conditions for a bow shock. Based on these findings, we conclude that the pressure discontinuity is likely the result of an ongoing major merger between two massive clusters. Since few observations of bow shocks in clusters have been made, this detection can contribute to the study of the dynamics of cluster mergers, which offers insight on how the most massive clusters may have formed.Peer reviewe

    Atmospheric Muon Flux at Sea Level, Underground, and Underwater

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    The vertical sea-level muon spectrum at energies above 1 GeV and the underground/underwater muon intensities at depths up to 18 km w.e. are calculated. The results are particularly collated with a great body of the ground-level, underground, and underwater muon data. In the hadron-cascade calculations, the growth with energy of inelastic cross sections and pion, kaon, and nucleon generation in pion-nucleus collisions are taken into account. For evaluating the prompt muon contribution to the muon flux, we apply two phenomenological approaches to the charm production problem: the recombination quark-parton model and the quark-gluon string model. To solve the muon transport equation at large depths of homogeneous medium, a semi-analytical method is used. The simple fitting formulas describing our numerical results are given. Our analysis shows that, at depths up to 6-7 km w. e., essentially all underground data on the muon intensity correlate with each other and with predicted depth-intensity relation for conventional muons to within 10%. However, the high-energy sea-level data as well as the data at large depths are contradictory and cannot be quantitatively decribed by a single nuclear-cascade model.Comment: 47 pages, REVTeX, 15 EPS figures included; recent experimental data and references added, typos correcte

    Final report on the search for neutrinoless double-ÎČ decay of 76Ge from the Gotthard underground experiment

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    We report here on the final results of a search for Ge-76 double-beta decay conducted in the Gotthard underground laboratory. The detector consists of an array of eight high-purity natural germanium crystals totaling 1095 cm^3 fiducial volume. The accumulated data set represents a sensitivity of 10.0 kg yr. No indication of neutrinoless double-beta decay was found. The measured half-life limits are T1/2(0+ --> 0+) > 6.0(3.3) x 10^(23) yr for the transition to the ground state and T1/2(0+ --> 2+) > 1.4(0.65) x 10^(23) yr for the transition to the first excited state at 68% (90%) C.L. From these results we derive an upper limit for the Majorana mass of the neutrino in the range of 1.8 to 6.7 eV depending on matrix-element calculations. The same results allow limits to be set for the right-handed-current parameters: < 2.2 x 10^(-8)

    New limit on neutrinoless double ÎČ decay in ^(136)Xe with a time projection chamber

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    A xenon time projection chamber with an active volume of 207 L has been built to study neutrinoless double ÎČ decay in ^(136)Xe. Data were taken in the Gotthard Underground Laboratory, with 5 atm of xenon enriched to 62.5% in ^(136)Xe. From 3380 h of data, no evidence has been found for the 0Îœ 0^(+)→0^(+) transition. Half-life limits of T_(1/2)^(0Îœ)>2.5(4.9)×10^(23) yr in the mass-mechanism mode and T_(1/2)^(0Îœ)>1.7(3.2)×10^(23) yr in the right-handed-current mode, at the 90(68)% C.L., were derived. An upper limit for the Majorana neutrino mass parameter was deduced

    Search for neutrinoless double-beta decay in 136-Xe with a time projection chamber

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    A xenon time projection chamber (TPC) with an active volume of 180 liters has been built to study neutrinoless double-beta decay in Xe-136. The experiment was performed in the Gotthard Underground Laboratory, with 5 atm of xenon enriched to 62.5% in Xe-136. The experimental details, background considerations, detector performance, and data analysis are discussed. From 6830 h of data, no evidence has been found for the 0nu 0+-->0+ transition. Half-life limits of T1/2(0nu) > 3.4(6.4) X 10^(23) yr in the mass mechanism mode, and T1/2(0nu) > 2.6(4.9) X 10^23 yr in the right-handed currents mode, at the 90(68)% C.L., were derived, corresponding to an upper limit on the Majorana neutrino mass parameter [m(nu)] of about 2.8 eV. Limits on two-neutrino double-beta decay of T1/2(2nu) /2 > 2. 1 X 10^(20) yr, and on neutrinoless double-beta decay with Majoron emission of T1/2(0nuchi) > 4.9 X 10^(21) yr, both at 90% C.L., were also derived. Accordingly, a limit on the effective Majoron-neutrino coupling parameter of [g(M)] < 2.4 X 10^(-4) was deduced

    Characterization of an extracellular lipase and its chaperone from Ralstonia eutropha H16

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    Lipase enzymes catalyze the reversible hydrolysis of triacylglycerol to fatty acids and glycerol at the lipid–water interface. The metabolically versatile Ralstonia eutropha strain H16 is capable of utilizing various molecules containing long carbon chains such as plant oil, organic acids, or Tween as its sole carbon source for growth. Global gene expression analysis revealed an upregulation of two putative lipase genes during growth on trioleate. Through analysis of growth and activity using strains with gene deletions and complementations, the extracellular lipase (encoded by the lipA gene, locus tag H16_A1322) and lipase-specific chaperone (encoded by the lipB gene, locus tag H16_A1323) produced by R. eutropha H16 was identified. Increase in gene dosage of lipA not only resulted in an increase of the extracellular lipase activity, but also reduced the lag phase during growth on palm oil. LipA is a non-specific lipase that can completely hydrolyze triacylglycerol into its corresponding free fatty acids and glycerol. Although LipA is active over a temperature range from 10 °C to 70 °C, it exhibited optimal activity at 50 °C. While R. eutropha H16 prefers a growth pH of 6.8, its extracellular lipase LipA is most active between pH 7 and 8. Cofactors are not required for lipase activity; however, EDTA and EGTA inhibited LipA activity by 83 %. Metal ions Mg[superscript 2+], Ca[superscript 2+], and Mn[superscript 2+] were found to stimulate LipA activity and relieve chelator inhibition. Certain detergents are found to improve solubility of the lipid substrate or increase lipase-lipid aggregation, as a result SDS and Triton X-100 were able to increase lipase activity by 20 % to 500 %. R. eutropha extracellular LipA activity can be hyper-increased, making the overexpression strain a potential candidate for commercial lipase production or in fermentations using plant oils as the sole carbon source.Malaysia-MIT Biotechnology Partnership Programm
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