排序方式: 共有37条查询结果,搜索用时 86 毫秒
1.
Lahaye T Koch T Fröhlich B Fattori M Metz J Griesmaier A Giovanazzi S Pfau T 《Nature》2007,448(7154):672-675
Symmetry-breaking interactions have a crucial role in many areas of physics, ranging from classical ferrofluids to superfluid (3)He and d-wave superconductivity. For superfluid quantum gases, a variety of new physical phenomena arising from the symmetry-breaking interaction between electric or magnetic dipoles are expected. Novel quantum phases in optical lattices, such as chequerboard or supersolid phases, are predicted for dipolar bosons. Dipolar interactions can also enrich considerably the physics of quantum gases with internal degrees of freedom. Arrays of dipolar particles could be used for efficient quantum information processing. Here we report the realization of a chromium Bose-Einstein condensate with strong dipolar interactions. By using a Feshbach resonance, we reduce the usual isotropic contact interaction, such that the anisotropic magnetic dipole-dipole interaction between 52Cr atoms becomes comparable in strength. This induces a change of the aspect ratio of the atom cloud; for strong dipolar interactions, the inversion of ellipticity during expansion (the usual 'smoking gun' evidence for a Bose-Einstein condensate) can be suppressed. These effects are accounted for by taking into account the dipolar interaction in the superfluid hydrodynamic equations governing the dynamics of the gas, in the same way as classical ferrofluids can be described by including dipolar terms in the classical hydrodynamic equations. Our results are a first step in the exploration of the unique properties of quantum ferrofluids. 相似文献
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Coulomb blockade and the Kondo effect in single-atom transistors 总被引:7,自引:0,他引:7
Park J Pasupathy AN Goldsmith JI Chang C Yaish Y Petta JR Rinkoski M Sethna JP Abruña HD McEuen PL Ralph DC 《Nature》2002,417(6890):722-725
Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect. 相似文献
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Establishing the age at death of individuals is an important step in their identification and can be done with high precision up to adolescence by analysis of dentition, but it is more difficult in adults. Here we show that the amount of radiocarbon present in tooth enamel as a result of nuclear bomb testing during 1955-63 is a remarkably accurate indicator of when a person was born. Age is determined to within 1.6 years, whereas the commonly used morphological evaluation of skeletal remains and tooth wear is sensitive to within 5-10 years in adults. 相似文献
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Rivas MA Beaudoin M Gardet A Stevens C Sharma Y Zhang CK Boucher G Ripke S Ellinghaus D Burtt N Fennell T Kirby A Latiano A Goyette P Green T Halfvarson J Haritunians T Korn JM Kuruvilla F Lagacé C Neale B Lo KS Schumm P Törkvist L;National Institute of Diabetes Digestive Kidney Diseases Inflammatory Bowel Disease Genetics Consortium 《Nature genetics》2011,43(11):1066-1073
More than 1,000 susceptibility loci have been identified through genome-wide association studies (GWAS) of common variants; however, the specific genes and full allelic spectrum of causal variants underlying these findings have not yet been defined. Here we used pooled next-generation sequencing to study 56 genes from regions associated with Crohn's disease in 350 cases and 350 controls. Through follow-up genotyping of 70 rare and low-frequency protein-altering variants in nine independent case-control series (16,054 Crohn's disease cases, 12,153 ulcerative colitis cases and 17,575 healthy controls), we identified four additional independent risk factors in NOD2, two additional protective variants in IL23R, a highly significant association with a protective splice variant in CARD9 (P < 1 × 10(-16), odds ratio ≈ 0.29) and additional associations with coding variants in IL18RAP, CUL2, C1orf106, PTPN22 and MUC19. We extend the results of successful GWAS by identifying new, rare and probably functional variants that could aid functional experiments and predictive models. 相似文献
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Cao J Schneeberger K Ossowski S Günther T Bender S Fitz J Koenig D Lanz C Stegle O Lippert C Wang X Ott F Müller J Alonso-Blanco C Borgwardt K Schmid KJ Weigel D 《Nature genetics》2011,43(10):956-963
The plant Arabidopsis thaliana occurs naturally in many different habitats throughout Eurasia. As a foundation for identifying genetic variation contributing to adaptation to diverse environments, a 1001 Genomes Project to sequence geographically diverse A. thaliana strains has been initiated. Here we present the first phase of this project, based on population-scale sequencing of 80 strains drawn from eight regions throughout the species' native range. We describe the majority of common small-scale polymorphisms as well as many larger insertions and deletions in the A. thaliana pan-genome, their effects on gene function, and the patterns of local and global linkage among these variants. The action of processes other than spontaneous mutation is identified by comparing the spectrum of mutations that have accumulated since A. thaliana diverged from its closest relative 10 million years ago with the spectrum observed in the laboratory. Recent species-wide selective sweeps are rare, and potentially deleterious mutations are more common in marginal populations. 相似文献
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Rosendahl J Witt H Szmola R Bhatia E Ozsvári B Landt O Schulz HU Gress TM Pfützer R Löhr M Kovacs P Blüher M Stumvoll M Choudhuri G Hegyi P te Morsche RH Drenth JP Truninger K Macek M Puhl G Witt U Schmidt H Büning C Ockenga J Kage A Groneberg DA Nickel R Berg T Wiedenmann B Bödeker H Keim V Mössner J Teich N Sahin-Tóth M 《Nature genetics》2008,40(1):78-82
Chronic pancreatitis is a persistent inflammatory disease of the pancreas, in which the digestive protease trypsin has a fundamental pathogenetic role. Here we have analyzed the gene encoding the trypsin-degrading enzyme chymotrypsin C (CTRC) in German subjects with idiopathic or hereditary chronic pancreatitis. Two alterations in this gene, p.R254W and p.K247_R254del, were significantly overrepresented in the pancreatitis group, being present in 30 of 901 (3.3%) affected individuals but only 21 of 2,804 (0.7%) controls (odds ratio (OR) = 4.6; confidence interval (CI) = 2.6-8.0; P = 1.3 x 10(-7)). A replication study identified these two variants in 10 of 348 (2.9%) individuals with alcoholic chronic pancreatitis but only 3 of 432 (0.7%) subjects with alcoholic liver disease (OR = 4.2; CI = 1.2-15.5; P = 0.02). CTRC variants were also found in 10 of 71 (14.1%) Indian subjects with tropical pancreatitis but only 1 of 84 (1.2%) healthy controls (OR = 13.6; CI = 1.7-109.2; P = 0.0028). Functional analysis of the CTRC variants showed impaired activity and/or reduced secretion. The results indicate that loss-of-function alterations in CTRC predispose to pancreatitis by diminishing its protective trypsin-degrading activity. 相似文献
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Simona Kavaliauskiene Carl-Martin Nymark Jonas Bergan Roger Simm Tuulia Sylvänne Helena Simolin Kim Ekroos Tore Skotland Kirsten Sandvig 《Cellular and molecular life sciences : CMLS》2014,71(6):1097-1116
Cell density is one of the extrinsic factors to which cells adapt their physiology when grown in culture. However, little is known about the molecular changes which occur during cell growth and how cellular responses are then modulated. In many cases, inhibitors, drugs or growth factors used for in vitro studies change the rate of cell proliferation, resulting in different cell densities in control and treated samples. Therefore, for a comprehensive data analysis, it is essential to understand the implications of cell density on the molecular level. In this study, we have investigated how lipid composition changes during cell growth, and the consequences it has for transport of Shiga toxin. By quantifying 308 individual lipid species from 17 different lipid classes, we have found that the levels and species distribution of several lipids change during cell growth, with the major changes observed for diacylglycerols, phosphatidic acids, cholesterol esters, and lysophosphatidylethanolamines. In addition, there is a reduced binding and retrograde transport of Shiga toxin in high density cells which lead to reduced intoxication by the toxin. In conclusion, our data provide novel information on how lipid composition changes during cell growth in culture, and how these changes can modulate intracellular trafficking. 相似文献
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Lorenzen ED Nogués-Bravo D Orlando L Weinstock J Binladen J Marske KA Ugan A Borregaard MK Gilbert MT Nielsen R Ho SY Goebel T Graf KE Byers D Stenderup JT Rasmussen M Campos PF Leonard JA Koepfli KP Froese D Zazula G Stafford TW Aaris-Sørensen K Batra P Haywood AM Singarayer JS Valdes PJ Boeskorov G Burns JA Davydov SP Haile J Jenkins DL Kosintsev P Kuznetsova T Lai X Martin LD McDonald HG Mol D Meldgaard M Munch K Stephan E Sablin M Sommer RS Sipko T Scott E Suchard MA Tikhonov A Willerslev R 《Nature》2011,479(7373):359-364
Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change. 相似文献