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排序方式: 共有93条查询结果,搜索用时 46 毫秒
41.
Aynajian P da Silva Neto EH Gyenis A Baumbach RE Thompson JD Fisk Z Bauer ED Yazdani A 《Nature》2012,486(7402):201-206
In solids containing elements with f orbitals, the interaction between f-electron spins and those of itinerant electrons leads to the development of low-energy fermionic excitations with a heavy effective mass. These excitations are fundamental to the appearance of unconventional superconductivity and non-Fermi-liquid behaviour observed in actinide- and lanthanide-based compounds. Here we use spectroscopic mapping with the scanning tunnelling microscope to detect the emergence of heavy excitations with lowering of temperature in a prototypical family of cerium-based heavy-fermion compounds. We demonstrate the sensitivity of the tunnelling process to the composite nature of these heavy quasiparticles, which arises from quantum entanglement of itinerant conduction and f electrons. Scattering and interference of the composite quasiparticles is used to resolve their energy-momentum structure and to extract their mass enhancement, which develops with decreasing temperature. The lifetime of the emergent heavy quasiparticles reveals signatures of enhanced scattering and their spectral lineshape shows evidence of energy-temperature scaling. These findings demonstrate that proximity to a quantum critical point results in critical damping of the emergent heavy excitation of our Kondo lattice system. 相似文献
42.
Dispersed human immunoglobulin kappa light-chain genes 总被引:11,自引:0,他引:11
E L?tscher K H Grzeschik H G Bauer H D Pohlenz B Straubinger H G Zachau 《Nature》1986,320(6061):456-458
The gene segments encoding the constant and variable regions of human immunoglobulin light chains of the kappa type (C kappa, V kappa) have been localized to chromosome 2. The distance between the C kappa and V kappa genes and the number of germline V kappa genes are unknown. As part of our work on the human V kappa locus, we have now mapped two solitary V kappa gene and a cluster of three V kappa genes to chromosomes 1, 15 and 22, respectively. The three genes that have been sequenced are nonprocessed pseudogenes, and the same may be true for the other two genes. This is the first time that V-gene segments have been found outside the C-gene-containing chromosomes. Our finding is relevant to current estimates of the size of the V kappa-gene repertoire. Furthermore, the dispersed gene regions have some unusual characteristics which may help to clarify the mechanism of dispersion. 相似文献
43.
Summary The influence of DTPA on the chromosome aberration rate of Chinese hamster cells in culture was studied. No increase of the aberration rate was observed after treatment with 10–2 and 10–3
M concentrations. 相似文献
44.
Curro NJ Caldwell T Bauer ED Morales LA Graf MJ Bang Y Balatsky AV Thompson JD Sarrao JL 《Nature》2005,434(7033):622-625
In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form (Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials--the copper oxides and a set of Ce- and U-based compounds. But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa5 has a transition temperature intermediate between those classes and therefore may bridge these extremes. Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa5, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials (a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered. 相似文献
45.
Israël G Szopa C Raulin F Cabane M Niemann HB Atreya SK Bauer SJ Brun JF Chassefière E Coll P Condé E Coscia D Hauchecorne A Millian P Nguyen MJ Owen T Riedler W Samuelson RE Siguier JM Steller M Sternberg R Vidal-Madjar C 《Nature》2005,438(7069):796-799
Aerosols in Titan's atmosphere play an important role in determining its thermal structure. They also serve as sinks for organic vapours and can act as condensation nuclei for the formation of clouds, where the condensation efficiency will depend on the chemical composition of the aerosols. So far, however, no direct information has been available on the chemical composition of these particles. Here we report an in situ chemical analysis of Titan's aerosols by pyrolysis at 600 degrees C. Ammonia (NH3) and hydrogen cyanide (HCN) have been identified as the main pyrolysis products. This clearly shows that the aerosol particles include a solid organic refractory core. NH3 and HCN are gaseous chemical fingerprints of the complex organics that constitute this core, and their presence demonstrates that carbon and nitrogen are in the aerosols. 相似文献
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48.
The chloroplast is the hallmark organelle of plants. It performs photosynthesis and is therefore required for photoautotrophic
plant growth. The chloroplast is the most prominent member of a family of related organelles termed plastids which are ubiquitous
in plant cells. Biogenesis of the chloroplast from undifferentiated proplastids is induced by light. The generally accepted
endosymbiont hypothesis states that chloroplasts have arisen from an internalized cyanobacterial ancestor. Although chloroplasts
have maintained remnants of the ancestral genome (plastome), the vast majority of the genes encoding chloroplast proteins
have been transferred to the nucleus. This poses two major challenges to the plant cell during chloroplast biogenesis: First,
light and developmental signals must be interpreted to coordinately express genetic information contained in two distinct
compartments. This is to ensure supply and stoichiometry of abundant chloroplast components. Second, developing chloroplasts
must efficiently import nuclear encoded and cytosolically synthesized proteins. A subset of proteins, including such encoded
by the plastome, must further be sorted to the thylakoid compartments for assembly into the photosynthetic apparatus.
Received 1 September 2000; received after revision 27 October 2000; accepted 1 November 2000 相似文献
49.
Rb targets histone H3 methylation and HP1 to promoters 总被引:78,自引:0,他引:78
Nielsen SJ Schneider R Bauer UM Bannister AJ Morrison A O'Carroll D Firestein R Cleary M Jenuwein T Herrera RE Kouzarides T 《Nature》2001,412(6846):561-565
50.