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Sökning: L773:0028 0836 OR L773:1476 4687 > (2010-2019) > (2011)

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1.
  • Alfoeldi, Jessica, et al. (författare)
  • The genome of the green anole lizard and a comparative analysis with birds and mammals
  • 2011
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 477:7366, s. 587-591
  • Tidskriftsartikel (refereegranskat)abstract
    • The evolution of the amniotic egg was one of the great evolutionary innovations in the history of life, freeing vertebrates from an obligatory connection to water and thus permitting the conquest of terrestrial environments(1). Among amniotes, genome sequences are available for mammals and birds(2-4), but not for non-avian reptiles. Here we report the genome sequence of the North American green anole lizard, Anolis carolinensis. We find that A. carolinensis microchromosomes are highly syntenic with chicken microchromosomes, yet do not exhibit the high GC and low repeat content that are characteristic of avian microchromosomes(2). Also, A. carolinensis mobile elements are very young and diverse-more so than in any other sequenced amniote genome. The GC content of this lizard genome is also unusual in its homogeneity, unlike the regionally variable GC content found in mammals and birds(5). We describe and assign sequence to the previously unknown A. carolinensis X chromosome. Comparative gene analysis shows that amniote egg proteins have evolved significantly more rapidly than other proteins. An anole phylogeny resolves basal branches to illuminate the history of their repeated adaptive radiations.
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2.
  • Andersson, Inger (författare)
  • Femtosecond X-ray protein nanocrystallography
  • 2011
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 470, s. 73-77
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded(1-3). It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction 'snapshots' are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source(4). We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes(5). More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (similar to 200 nm to 2 mm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes(6). This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage.
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3.
  • Andersson, Inger (författare)
  • Single mimivirus particles intercepted and imaged with an X-ray laser
  • 2011
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 470, s. 78-81
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray lasers offer new capabilities in understanding the structure of biological systems, complex materials and matter under extreme conditions(1-4). Very short and extremely bright, coherent X-ray pulses can be used to outrun key damage processes and obtain a single diffraction pattern from a large macromolecule, a virus or a cell before the sample explodes and turns into plasma(1). The continuous diffraction pattern of non-crystalline objects permits oversampling and direct phase retrieval(2). Here we show that high-quality diffraction data can be obtained with a single X-ray pulse from a noncrystalline biological sample, a single mimivirus particle, which was injected into the pulsed beam of a hard-X-ray free-electron laser, the Linac Coherent Light Source(5). Calculations indicate that the energy deposited into the virus by the pulse heated the particle to over 100,000 K after the pulse had left the sample. The reconstructed exit wavefront (image) yielded 32-nm full-period resolution in a single exposure and showed no measurable damage. The reconstruction indicates inhomogeneous arrangement of dense material inside the virion. We expect that significantly higher resolutions will be achieved in such experiments with shorter and brighter photon pulses focused to a smaller area. The resolution in such experiments can be further extended for samples available in multiple identical copies.
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4.
  • Arner, Peter, et al. (författare)
  • Dynamics of human adipose lipid turnover in health and metabolic disease
  • 2011
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 478:7367, s. 110-113
  • Tidskriftsartikel (refereegranskat)abstract
    • Adipose tissue mass is determined by the storage and removal of triglycerides in adipocytes(1). Little is known, however, about adipose lipid turnover in humans in health and pathology. To study this in vivo, here we determined lipid age by measuring (14)C derived from above ground nuclear bomb tests in adipocyte lipids. We report that during the average ten-year lifespan of human adipocytes, triglycerides are renewed six times. Lipid age is independent of adipocyte size, is very stable across a wide range of adult ages and does not differ between genders. Adipocyte lipid turnover, however, is strongly related to conditions with disturbed lipid metabolism. In obesity, triglyceride removal rate (lipolysis followed by oxidation) is decreased and the amount of triglycerides stored each year is increased. In contrast, both lipid removal and storage rates are decreased in non-obese patients diagnosed with the most common hereditary form of dyslipidaemia, familial combined hyperlipidaemia. Lipid removal rate is positively correlated with the capacity of adipocytes to break down triglycerides, as assessed through lipolysis, and is inversely related to insulin resistance. Our data support a mechanism in which adipocyte lipid storage and removal have different roles in health and pathology. High storage but low triglyceride removal promotes fat tissue accumulation and obesity. Reduction of both triglyceride storage and removal decreases lipid shunting through adipose tissue and thus promotes dyslipidaemia. We identify adipocyte lipid turnover as a novel target for prevention and treatment of metabolic disease.
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5.
  • Blicharska, Malgorzata, et al. (författare)
  • Think bigger for conservation
  • 2011
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 470, s. 39-39
  • Annan publikation (övrigt vetenskapligt)
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6.
  • Breimer, LH, et al. (författare)
  • Mobility rethought
  • 2011
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 470
  • Tidskriftsartikel (refereegranskat)
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7.
  • Cardinale, Massimiliano (författare)
  • Fishery reform: many stocks secure
  • 2011
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 476, s. 282-282
  • Annan publikation (refereegranskat)
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8.
  • Cederwall, Bo, et al. (författare)
  • Evidence for a spin-aligned neutron-proton paired phase from the level structure of 92Pd
  • 2011
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 469:7328, s. 68-71
  • Tidskriftsartikel (refereegranskat)abstract
    • Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work(1) that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing(2-6), in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus Pd-92. Gamma rays emitted following the Ni-58(Ar-36,2n)Pd-92 fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution c-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction(2-6). We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling(7,8)) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
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9.
  • Cederwall, B., et al. (författare)
  • Evidence for a spin-aligned neutron-proton paired phase from the level structure of Pd-92
  • 2011
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 469:7328, s. 68-71
  • Tidskriftsartikel (refereegranskat)abstract
    • Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work(1) that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing(2-6), in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus Pd-92. Gamma rays emitted following the Ni-58(Ar-36,2n)Pd-92 fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution c-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction(2-6). We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling(7,8)) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
  •  
10.
  • Larsson, Josefin, et al. (författare)
  • X-ray illumination of the ejecta of supernova 1987A
  • 2011
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 474:7352, s. 484-486
  • Tidskriftsartikel (refereegranskat)abstract
    • When a massive star explodes as a supernova, substantial amounts of radioactive elements-primarily (56)Ni, (57)Ni and (44)Ti-are produced(1). After the initial flash of light from shock heating, the fading light emitted by the supernova is due to the decay of these elements(2). However, after decades, the energy powering a supernova remnant comes from the shock interaction between the ejecta and the surrounding medium(3). The transition to this phase has hitherto not been observed: supernovae occur too infrequently in the Milky Way to provide a young example, and extragalactic supernovae are generally too faint and too small. Here we report observations that show this transition in the supernova SN 1987A in the Large Magellanic Cloud. From 1994 to 2001, the ejecta faded owing to radioactive decay of (44)Ti as predicted. Then the flux started to increase, more than doubling by the end of 2009. We show that this increase is the result of heat deposited by X-rays produced as the ejecta interacts with the surrounding material. In time, the X-rays will penetrate farther into the ejecta, enabling us to analyse the structure and chemistry of the vanished star.
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