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- Tanvir, N. R., et al.
(författare)
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A γ-ray burst at a redshift of z~8.2
- 2009
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 461, s. 1254-1257
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Tidskriftsartikel (refereegranskat)abstract
- Long-duration γ-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z>20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-α emitting galaxy. Here we report that GRB090423 lies at a redshift of z~8.2, implying that massive stars were being produced and dying as GRBs ~630Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.
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- Barthelmy, S D, et al.
(författare)
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An origin for short gamma-ray bursts unassociated with current star formation
- 2005
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 438, s. 994-996
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Tidskriftsartikel (refereegranskat)abstract
- Two short (< 2 s) gamma-ray bursts (GRBs) have recently been localized(1-4) and fading afterglow counterparts detected(2-4). The combination of these two results left unclear the nature of the host galaxies of the bursts, because one was a star-forming dwarf, while the other was probably an elliptical galaxy. Here we report the X-ray localization of a short burst (GRB 050724) with unusual gamma-ray and X-ray properties. The X-ray afterglow lies off the centre of an elliptical galaxy at a redshift of z = 0.258 (ref. 5), coincident with the position determined by ground-based optical and radio observations(6-8). The low level of star formation typical for elliptical galaxies makes it unlikely that the burst originated in a supernova explosion. A supernova origin was also ruled out for GRB 050709 ( refs 3, 31), even though that burst took place in a galaxy with current star formation. The isotropic energy for the short bursts is 2 - 3 orders of magnitude lower than that for the long bursts. Our results therefore suggest that an alternative source of bursts - the coalescence of binary systems of neutron stars or a neutron star-black hole pair - are the progenitors of short bursts.
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- Göransson, Olga, et al.
(författare)
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Mechanism of action of A-769662, a valuable tool for activation of AMP-activated protein kinase
- 2007
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 282:45, s. 32549-32560
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the mechanism of A- 769662, a new activator of AMP- activated protein kinase ( AMPK). Unlike other pharmacological activators, it directly activates native rat AMPK by mimicking both effects of AMP, i. e. allosteric activation and inhibition of dephosphorylation. We found that it has no effect on the isolated alpha subunit kinase domain, with or without the associated autoinhibitory domain, or on interaction of glycogen with the beta subunit glycogen- binding domain. Although it mimics actions of AMP, it has no effect on binding of AMP to the isolated Bateman domains of the gamma subunit. The addition of A- 769662 to mouse embryonic fibroblasts or primary mouse hepatocytes stimulates phosphorylation of acetyl- CoA carboxylase ( ACC), effects that are completely abolished in AMPK- alpha 1(-/-) alpha 2(-/-) cells but not in TAK1(-/-) mouse embryonic fibroblasts. Phosphorylation of AMPK and ACC in response to A- 769662 is also abolished in isolated mouse skeletal muscle lacking LKB1, a major upstream kinase for AMPK in this tissue. However, in HeLa cells, which lack LKB1 but express the alternate upstream kinase calmodulin- dependent protein kinase kinase-beta, phosphorylation of AMPK and ACC in response to A- 769662 still occurs. These results show that in intact cells, the effects of A- 769662 are independent of the upstream kinase utilized. We propose that this direct and specific AMPK activator will be a valuable experimental tool to understand the physiological roles of AMPK.
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| 12. |
- Sakamoto, K., et al.
(författare)
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P Cygni Profiles of Molecular Lines Toward Arp 220 Nuclei
- 2009
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Ingår i: Astrophysical Journal Letters. - 2041-8213 .- 2041-8205. ; 700:2, s. L104-L108
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Tidskriftsartikel (refereegranskat)abstract
- We report ~100 pc (0farcs3) resolution observations of (sub)millimeter HCO+ and CO lines in the ultraluminous infrared galaxy Arp 220. The lines peak at two merger nuclei, with HCO+ being more spatially concentrated than CO. Asymmetric line profiles with blueshifted absorption and redshifted emission are discovered in HCO+(3-2) and (4-3) toward the two nuclei and in CO(3-2) toward one nucleus. We suggest that these P Cygni profiles are due to ~100 km s–1 outward motion of molecular gas from the nuclei. This gas is most likely outflowing from the inner regions of the two nuclear disks rotating around individual nuclei, clearing the shroud around the luminosity sources there.
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| 13. |
- Sakamoto, Kazuyuki, et al.
(författare)
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Surface electronic structures of the Eu- and Ca-induced so-called Si(111)-(5×1) reconstructions
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:23, s. 235311-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electronic structures of the so-called Eu- and Ca-induced Si(111)-(5×1) surfaces by using angle-resolved photoelectron spectroscopy (ARPES) and low-energy electron diffraction (LEED). The LEED patterns of these surfaces indicate that the periodicities of both surfaces are actually (5×4). In the ARPES study, seven surface states were observed on each (5×4) reconstruction. Of these surface states, the dispersions of five of them show good agreement with those of the Eu- and Ca-induced (3×2) honeycomb-chain-channel (HCC) surfaces and the dispersions of the two other states agree well with those of the Eu- and Ca-induced (2×1) Seiwatz surfaces along the [1̅ 10] direction—i.e., the direction parallel to the adsorbate chain. Taking the dispersion behavior of these surface states into account, we conclude that the interaction between the nearest-neighbor HCC chain and Seiwatz chain is quite small and that the electronic structure of one chain hardly affects the electronic structure of its neighboring chain. We also discuss the atomic structure of the Eu- and Ca-induced Si(111)-(5×1) reconstructions based on their electronic structures.
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| 14. |
- Sakamoto, K., et al.
(författare)
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Surface electronic structures of the Eu-induced Si(111)-(3×2) and -(2×1) reconstructions
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:4, s. 045310-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structures of the Eu∕Si(111)-(3×2) and (2×1) surfaces have been investigated by angle-resolved photoelectron spectroscopy. On the (3×2) surface, we identify six surface states in the gap and a pocket of the bulk band projection. Among the five surface states observed in the bulk band gap, the dispersions of three of them agree well with those of the surface states of monovalent atom adsorbed Si(111)-(3×1) surfaces. The dispersions of the two other surface states observed in the band gap agree well with those observed on the Ca∕Si(111)-(3×2) surface, which has basically the same structure as that of monovalent atom adsorbed Si(111)-(3×1) surfaces. Taking these results into account, we conclude that the five surface states observed in the band gap originate from the orbitals of Si atoms that form a honeycomb-chain-channel structure. In the case of the (2×1) surface, two semiconducting states are observed in the bulk band gap. The difference in binding energy of these two states at the Γ̅ point agrees well with that of the surface states obtained theoretically for a clean Si(111)-(2×1) surface with a Seiwatz structure, and the dispersion of the upper state shows good agreement with the corresponding theoretical surface state. These observations indicate that the two surface states in the band gap originate from Si atoms that form a Seiwatz chain. The present results support the structures of the Eu∕Si(111)-(3×2) and (2×1) surfaces proposed in the literature.
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