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181.
Spin-orbit (SO) coupling--the interaction between a quantum particle's spin and its momentum--is ubiquitous in physical systems. In condensed matter systems, SO coupling is crucial for the spin-Hall effect and topological insulators; it contributes to the electronic properties of materials such as GaAs, and is important for spintronic devices. Quantum many-body systems of ultracold atoms can be precisely controlled experimentally, and would therefore seem to provide an ideal platform on which to study SO coupling. Although an atom's intrinsic SO coupling affects its electronic structure, it does not lead to coupling between the spin and the centre-of-mass motion of the atom. Here, we engineer SO coupling (with equal Rashba and Dresselhaus strengths) in a neutral atomic Bose-Einstein condensate by dressing two atomic spin states with a pair of lasers. Such coupling has not been realized previously for ultracold atomic gases, or indeed any bosonic system. Furthermore, in the presence of the laser coupling, the interactions between the two dressed atomic spin states are modified, driving a quantum phase transition from a spatially spin-mixed state (lasers off) to a phase-separated state (above a critical laser intensity). We develop a many-body theory that provides quantitative agreement with the observed location of the transition. The engineered SO coupling--equally applicable for bosons and fermions--sets the stage for the realization of topological insulators in fermionic neutral atom systems. 相似文献
182.
183.
Lissauer JJ Fabrycky DC Ford EB Borucki WJ Fressin F Marcy GW Orosz JA Rowe JF Torres G Welsh WF Batalha NM Bryson ST Buchhave LA Caldwell DA Carter JA Charbonneau D Christiansen JL Cochran WD Desert JM Dunham EW Fanelli MN Fortney JJ Gautier TN Geary JC Gilliland RL Haas MR Hall JR Holman MJ Koch DG Latham DW Lopez E McCauliff S Miller N Morehead RC Quintana EV Ragozzine D Sasselov D Short DR Steffen JH 《Nature》2011,470(7332):53-58
When an extrasolar planet passes in front of (transits) its star, its radius can be measured from the decrease in starlight and its orbital period from the time between transits. Multiple planets transiting the same star reveal much more: period ratios determine stability and dynamics, mutual gravitational interactions reflect planet masses and orbital shapes, and the fraction of transiting planets observed as multiples has implications for the planarity of planetary systems. But few stars have more than one known transiting planet, and none has more than three. Here we report Kepler spacecraft observations of a single Sun-like star, which we call Kepler-11, that reveal six transiting planets, five with orbital periods between 10 and 47?days and a sixth planet with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases. The degree of coplanarity and proximity of the planetary orbits imply energy dissipation near the end of planet formation. 相似文献
184.
Spatio-temporal transcriptome of the human brain 总被引:1,自引:0,他引:1
185.
Quantum metrology aims to use entanglement and other quantum resources to improve precision measurement. An interferometer using N independent particles to measure a parameter χ can achieve at best the standard quantum limit of sensitivity, δχ?∝?N(-1/2). However, using N entangled particles and exotic states, such an interferometer can in principle achieve the Heisenberg limit, δχ?∝?N(-1). Recent theoretical work has argued that interactions among particles may be a valuable resource for quantum metrology, allowing scaling beyond the Heisenberg limit. Specifically, a k-particle interaction will produce sensitivity δχ?∝?N(-k) with appropriate entangled states and δχ?∝?N(-(k-1/2)) even without entanglement. Here we demonstrate 'super-Heisenberg' scaling of δχ?∝?N(-3/2) in a nonlinear, non-destructive measurement of the magnetization of an atomic ensemble. We use fast optical nonlinearities to generate a pairwise photon-photon interaction (corresponding to k = 2) while preserving quantum-noise-limited performance. We observe super-Heisenberg scaling over two orders of magnitude in N, limited at large numbers by higher-order nonlinear effects, in good agreement with theory. For a measurement of limited duration, super-Heisenberg scaling allows the nonlinear measurement to overtake in sensitivity a comparable linear measurement with the same number of photons. In other situations, however, higher-order nonlinearities prevent this crossover from occurring, reflecting the subtle relationship between scaling and sensitivity in nonlinear systems. Our work shows that interparticle interactions can improve sensitivity in a quantum-limited measurement, and experimentally demonstrates a new resource for quantum metrology. 相似文献
186.
187.
Sicardy B Ortiz JL Assafin M Jehin E Maury A Lellouch E Hutton RG Braga-Ribas F Colas F Hestroffer D Lecacheux J Roques F Santos-Sanz P Widemann T Morales N Duffard R Thirouin A Castro-Tirado AJ Jelínek M Kubánek P Sota A Sánchez-Ramírez R Andrei AH Camargo JI da Silva Neto DN Gomes AR Martins RV Gillon M Manfroid J Tozzi GP Harlingten C Saravia S Behrend R Mottola S Melendo EG Peris V Fabregat J Madiedo JM Cuesta L Eibe MT Ullán A Organero F Pastor S de Los Reyes JA Pedraz S Castro A 《Nature》2011,478(7370):493-496
The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1?AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163?±?6?kilometres, density 2.52?±?0.05 grams per cm(3) and a high visible geometric albedo, Pv = 0.96(+0.09)(-0.04). No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1?nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun. 相似文献
188.
B. C. Yoo S-H. Hong J-L. Ku Y-H. Kim Y-K. Shin S-G. Jang I-J. Kim S-Y. Jeong J-G. Park 《Cellular and molecular life sciences : CMLS》2009,66(2):350-364
Comparative analysis of proteomes using 5-fluorouracil (5-FU)-resistant human colon cancer cell line revealed that decreased
galectin-3 expression was significantly associated with retarded proliferation. However, in the presence of 5-FU proliferation
rate of cells with suppressed galectin-3 expression did not differ from that of cells with normal galectin-3 expression, even
galectin-3 suppression augmented apoptosis. Mechanism by which galectin-3 regulates cancer cell proliferation has been identified
in immunoprecipitates of the anti-galectin-3 antibody. Heterogeneous nuclear ribonucleoprotein Q (hnRNP Q) was identified
as a protein interacting with galectin-3. Interestingly, while galectin-3 protein was not affected by the hnRNP Q level, its
suppression was accompanied by a decrease in hnRNP Q expression. The present study demonstrates that galectin-3 stabilizes
hnRNP Q via complex formation, and reduction in the hnRNP Q level leads to slow proliferation and less susceptibility to 5-FU.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
B.C.Yoo; S-H.Hong; These two authors contributed equally to this work.
Received 10 September 2008; received after revision 19 October 2008; accepted 07 November 2008 相似文献
189.
J. Kim D. C. Han J. M. Kim S. Y. Lee S. J. Kim J. R. Woo J. W. Lee S.-K. Jung K. S. Yoon H. G. Cheon S. S. Kim S. H. Hong B.-M. Kwon 《Cellular and molecular life sciences : CMLS》2009,66(10):1766-1781
Indenone KR-62776 acts as an agonist of PPARγ without inducing obesity in animal models and cells. X-ray crystallography reveals
that the indenone occupies the binding pocket in a different manner than rosiglitazone. 2-Dimensional gel-electrophoresis
showed that the expression of 42 proteins was altered more than 2.0-fold between KR-62776- or rosiglitazone-treated adipocyte
cells and control cells. Rosiglitazone down-regulated the expression of ERK1/2 and suppressed the phosphorylation of ERK1/2
in these cells. However, the expression of ERK1/2 was up-regulated in KR-62776-treated cells. Phosphorylated ERK1/2, activated
by indenone, affects the localization of PPARγ, suggesting a mechanism for indenone-inhibition of adipogenesis in 3T3-L1 preadipocyte
cells. The preadipocyte cells are treated with ERK1/2 inhibitor PD98059, a large amount of the cells are converted to adipocyte
cells. These results support the conclusion that the localization of PPARγ is one of the key factors explaining the biological
responses of the ligands.
Received 04 March 2009; received after revision 13 March 2009; accepted 17 March 2009 相似文献
190.
Apolipoprotein M (apoM) is a novel apolipoprotein found mainly in high-density lipoproteins (HDL). Its function is yet to
be defined. ApoM (25 kDa) has a typical lipocalin ?-barrel fold and a hydrophobic pocket. Retinoids bind apoM but with low
affinity and may not be the natural ligands. ApoM retains its signal peptide, which serves as a hydrophobic anchor to the
lipoproteins. This prevents apoM from being lost in the urine. Approximately 5% of HDL carries an apoM molecule. ApoM in plasma
(1 μM) correlates strongly with both low-density lipoprotein (LDL) and HDL cholesterol, suggesting a link to cholesterol metabolism.
However, in casecontrol studies, apoM levels in patients with coronary heart disease (CHD) and controls were similar, suggesting
apoM levels not to affect the risk for CHD in humans. Experiments in transgenic mice suggested apoM to have antiatherogenic
properties; possible mechanisms include increased formation of pre-? HDL, enhanced cholesterol mobilization from foam cells,
and increased antioxidant properties.
Received 28 November 2008; received after revision 15 December 2008; accepted 16 December 2008 相似文献